FLUORESCENT OXYGEN CHANNELING IMMUNOASSAYS

Abstract: Methods are disclosed for determining an analyte in a medium suspected of containing the analyte. One method comprises treating a medium suspected of containing an analyte under conditions such that the analyte, if present, causes a photosensitizer and a photoactive indicator precursor molecule to come into close proximity. The photosensitizer generates singlet oxygen which activates the photoactive indicator precursor to generate a photoactive indicator molecule. Upon irradiation with light the photoactive indicator molecule produces light, which is measured. The amount of light produced by the photoactive indicator is related to the amount of analyte in the medium. Compositions, kits, and compounds are also disclosed.

Description: FLU0RESCENT OXYGEN CHANNELING IMMDNOASSAYS BACKGROUND OF THE INVENTION Field of the Invention This invention relates to methods, compositions and kits for determining an analyte in a sample. In particular, this invention relates to specific binding assays which utilize a photoactive indicator precursor which can react with singlet oxygen to form a fluorescent product. The clinical diagnostic field has seen a broad expansion in recent years, both as to the variety of materials (analytes) that may be readily and accurately determined, as well as the methods for the determination. Convenient, reliable and non-hazardous means for detecting the presence of low concentrations of materials in liquids is desired. In clinical chemistry these materials may be present in body fluids in concentrations below 10" 12 molar. The difficulty of detecting low concentrations of these materials is enhanced by the relatively small sample sizes that can be utilized. In developing an assay there are many considerations. One consideration is the signal response to changes in the concentration of an analyte. A second consideration is the ease with which the protocol for the assay may be carried out. A third consideration is the variation in interference from sample to sample. Ease of preparation and purification of the reagents, availability of equipment, ease of automation and interaction with material of interest are some of the additional considerations in developing a useful assay. One broad category of techniques involves the use of a receptor which can specifically bind to a particular spacial and polar organization of a labeled ligand as a function of the presence of an analyte. The observed effect of binding by the receptor will depend upon the label. In some instances the binding of the receptor merely provides for a differentiation in molecular weight between bound and unbound labeled ligand. In other instances the binding of the receptor will facilitate separation of bound labeled ligand from free labeled ligand or it may affect the nature of the signal obtained from the label so that the signal varies with the amount of receptor bound to labeled ligand. A further variation is that the receptor is labeled and the ligand unlabeled. Alternatively, both the receptor and ligand are labeled or different receptors are labeled with two different labels, whereupon the labels interact when in close proximity and the amount of ligand present affects the degree to which the labels of the receptor may interact. There is a continuing need for new and accurate techniques that can be adapted for a wide spectrum of different ligands or be used in specific cases where other methods may not be readily adaptable. Homogeneous immunoassays in which it is unnecessary to separate the bound and unbound label have previously been described for small molecules. These assays include SYVA's FRAT ® assay, EMIT ® assay, enzyme channeling im unoassay, and fluorescence energy transfer immunoassay (FETI) ; enzyme inhibitor immunoassays (Hoffmann LaRoche aind Abbott Laboratories) : fluorescence polarization immunoassay (Dandlicker) , among others. All of these methods have limited sensitivity, and only a few including FETI and enzyme channeling, are suitable for large multiepitopic analytes. Heterogenous immunoassays in which a separation step is required are generally useful for both small and large molecules. Various labels have been used including enzymes (ELISA) , fluorescent labels (FIA) , radiolabels (RIA) , chemiluminescent labels (CLA) , etc. Luminescent compounds, such as fluorescent compounds and chemiluminescent compounds, find wide application in the assay field because of their ability to emit light. For this reason, luminescers have been utilized as labels in assays such as nucleic acid assays and immunoassays. For example, a member of a specific binding pair is conjugated to a luminescer and various protocols are employed. The luminescer conjugate can be partitioned between a solid phase and a liquid phase in relation to the amount of analyte in a sample suspected of containing the analyte. By measuring the luminescence of either of the phases, one can relate the level of luminescence observed to a concentration of the analyte in the sample. Particles, such as latex beads and liposomes, have also been utilized in assays. For example, in homogeneous assays an enzyme may be entrapped in the aqueous phase of a liposome labelled with an antibody or antigen. The liposomes are caused to release the enzyme in the presence of a sample and complement. Antibody- or antigen-labelled liposomes, having water soluble fluorescent or non-fluorescent dyes encapsulated within an aqueous phase or lipid soluble dyes dissolved in the lipid bilayer of the lipid vesicle, have also been utilized to assay for analytes capable of entering into an immunochemical reaction with the surface bound antibody or antigen. Detergents have been used to release the dyes from the aqueous phase of the liposomes. Particles have been dyed with fluorescent dyes and used as labels in immunoassays. Undyed particles have also been used (e.g. , latex agglutination) . Related Art European Published Patent Application No. 0 345 776 (McCapra) discloses specific binding assays that utilize a sensitizer as a label. The sensitizers include any moiety which, when stimulated by excitation with radiation of one or more wavelengths or other chemical or physical stimulus (e.g., electron transfer, electrolysis, electroluminescence or energy transfer) will achieve an excited state which (a) upon interaction with molecular oxygen will produce singlet molecular oxygen, or (b) upon interaction with a leuco dye will assume a reduced form that can be returned to its original unexcited state by interaction with molecular oxygen resulting in the production of hydrogen peroxide. Either interaction with the excited senεitizer will, with the addition of reagents, produce a detectible signal. European Published Patent Application No. 0 476 556 (Motsenbocker) discloses a method for determination of a light sensitive substance wherein irradiation of lumigenic substance-light sensitive substance solution with modulated light is used to generate short wavelength light proportionally to the concentration of the light sensitive substance. Luminescent labels for immunoassays are described in McCapra et al., Journal of Bioluminescence and Chemiluminescence (1989), Vol. 4, pp. 51-58. European Published Patent Application No. 0 515 194 (ϋllman et al.) discloses methods for determining an analyte in a medium suspected of containing the analyte. One such disclosed method comprises treating a medium suspected of containing an analyte under conditions such that the analyte, if present, causes a photosensitizer and a chemiluminescent compound to come into close proximity. The photosensitizer generates singlet oxygen and activates the chemiluminescent compound when it is in close proximity. The activated chemiluminescent subsequently produces light upon activation by singlet oxygen. The amount of light produced is related to the amount of einalyte in the medium. In this method, each singlet oxygen that is generated can react with no more than one chemiluminescent compound, which, in turn, can emit not more than one photon of light. The sensitivity of the method is therefore limited by the chemiluminescence quantum efficiency of the chemiluminescent compound, and, more importantly, by the ability to detect the limited number of photons that will be emitted upon reaction with singlet oxygen. SUMMARY OF THE INVENTION The present invention is directed to methods for determining an analyte, kits for conducting assays for an analyte, and compounds useful in the methods and assays. One aspect of the invention is a method for determining an analyte which is a specific binding pair (sbp) member. In one embodiment of this aspect the method comprises a first step of providing in combination a medium suspected of containing an analyte; a photosensitizer capable in its excited state of generating singlet oxygen, wherein the photosensitizer is associated with an sbp member; and a photoactive indicator precursor capable of forming a photoactive indicator upon reaction with singlet oxygen, wherein the photoactive indicator precursor is associated with an sbp member; then a second step of exciting the photosensitizer by irradiation with light; and a final step of measuring the fluorescence of the photoactive indicator. At least one of the sbp members is capable of binding directly or indirectly to the analyte or to an sbp member complementary to the analyte. The fluorescence measured is related to the amount of the analyte in the medium. In another embodiment, the method comprises the first step of combining in an aqueous medium a sample suspected of containing an analyte; a first suspendible particle comprised of a photosensitizer capable in its excited state of generating singlet oxygen, wherein the particle has a specific binding pair (sbp) member bound thereto; and a second suspendible particle comprised of a photoactive indicator precursor capable of forming a photoactive indicator upon reaction with singlet oxygen, wherein the particle has an sbp member bound thereto; a second step of irradiating the medium to excite the photosensitizer to generate singlet oxygen; and a final step of measuring the fluorescence of the photoactive indicator. Each sbp member is capable of binding directly or indirectly with the analyte or to an sbp member complementary to the analyte. The fluorescence measured is related to the amount of the analyte in the medium. In another embodiment, the method comprises a first step of providing in combination a medium suspected of containing an analyte; a photosensitizer capable in its excited state of generating singlet oxygen, wherein the photosensitizer is associated with an sbp member; and a suspendible particle having bound thereto an sbp member, wherein the suspendible particle comprises a photoactive indicator precursor capable of forming a photoactive indicator upon reaction with singlet oxygen; a second step of irradiating the combination with light to excite the photosensitizer; and a final step of measuring the fluorescence of the photoactive indicator. Each sbp member is capable of binding directly or indirectly to the analyte or to an sbp member complementary to the analyte. The fluorescence measured is related to the amount of the analyte in the medium. Another aspect of the invention is a method for determining an analyte. The method comprises a first step of providing in combination a medium suspected of containing an analyte; a photosensitizer capable in its excited state of generating singlet oxygen, wherein the photosensitizer is associated with a first specific binding pair (sbp) member; and a photoactive indicator precursor capable of forming a photoactive indicator upon reaction with singlet oxygen, wherein the photoactive indicator precursor is associated with a second sbp member; a second step of irradiating the combination with light to excite the photosensitizer; and a final step of measuring the fluorescence of the photoactive indicator. Each sbp member is capable of binding directly or indirectly to the analyte or to an sbp member complementary to the analyte. The fluorescence measured is related to the amount of the analyte in the medium. Another aspect of this invention is a method for determining a polynucleotide einalyte. The method comprises a first step of combining in an aqueous medium the analyte; one or more polynucleotide probes (wherein each probe contains a nucleotide sequence complementary to a nucleotide sequence of the Einalyte and wherein at least one probe is associated with a specific binding pair (sbp) member that is differenct from said complementary nucleotide sequence) ; a photosensitizer capable in its excited state of generating singlet oxygen (wherein said photosensitizer is associated with a polynucleotide having a sequence complementary to a nucleotide sequence of said probe) ; and a photoactive indicator precursor capable of forming a photoactive indicator upon reaction with singlet oxygen, wherein the photoactive indicator precursor is associated with an sbp member complementary to the sbp member associated with the probe; a second step of irradiating the medium with light to excite the photosensitizer to generate singlet oxygen; and a third step of measuring the fluorescence of the photoactive indicator. The fluorescence is related to the amount of the analyte in the medium. A method for determining an analyte, which method comprises (A) if the analyte is a polynucleotide (a) combining in an aqueous medium (1) said analyte; (2) one or more polynucleotide probes, wherein each probe contains a nucleotide sequence complementary to a nucleotide sequence of said analyte and wherein at least one probe is bound to a specific binding pair (sbp) member, or is bound to or incorporated in a particle having said sbp member incorporated therein or bound thereto, said sbp member being different from said complementary nucleotide sequence; (3) a photosensitizer capable in its excited state of generating singlet oxygen, wherein said photosensitizer is bound to, or is bound to or incorporated in a particle having incorporated therein or bound thereto, a nucleotide sequence complementary to a nucleotide sequence of said probe; and (4) a photoactive indicator precursor capable of forming a photoactive indicator upon reaction with singlet oxygen, wherein said photoactive indicator precursor is bound to, or is bound to or incorporated in a particle having incorporated therein or bound thereto, an sbp member complementary to said sbp member associated with said probe; (b) irradiating said medium with light to excite said photosensitizer to generate singlet oxygen; and (c) measuring the fluorescence of said photoactive indicator; wherein said fluorescence is related to the amount of said analyte in said medium; or (B) if the analyte is other than a polynucleotide (a) providing in combination: (1) a medium suspected of containing an einalyte; (2) a photosensitizer capable in its excited state of generating singlet oxygen, wherein said photosensitizer is bound to, or is bound to or incorporated in a particle having incorporated therein or bound thereto, a first specific binding pair (sbp) member; and (3) a photoactive indicator precursor capable of forming a photoactive indicator upon reaction with singlet oxygen, wherein said photoactive indicator precursor is bound to, or is bound to or incorporated in a particle having incorporated therein or bound thereto, a second sbp member; (b) irradiating said combination with light to excite said photosensitizer; and (c) measuring the fluorescence of said photoactive indicator; wherein each sbp member is capable of binding directly or indirectly to said analyte or to an sbp member complementary to said analyte, and wherein said fluorescence is related to the amount of said analyte in said medium, and wherein said photosensitizer is optionally part of a suspendible particle to which said first sbp member is bound, and wherein said photoactive indicator precursor is optionally part of a suspendible particle to which said second sbp member is bound. Another aspect of this invention is a composition comprising suspendible particles of average diameter of 20 to 4000 nanometers having associated therewith a photoactive indicator precursor, wherein the photoactive indicator precursor contains a selenium or tellurium atom. Another aspect of this invention is a kit for conducting an assay for analyte. The kit comprises, in packaged combination, suspendible particles comprising a photoactive indicator precursor, wherein said photoactive indicator precursor contains a selenium or a tellurium atom and wherein the particles have bound thereto an sbp member; and a photosensitizer which is associated with an sbp member and is capable in its excited state of activating oxygen to its singlet state, wherein at least one of the sbp members is capable of binding to the analyte or to an sbp member complementary to the analyte. In another embodiment of this aspect, the kit comprises, in packaged combination, a composition, which comprises a first suspendible particle comprising a photoactive indicator precursor containing a selenium or tellurium atom, wherein the first particle has bound thereto an sbp member; and a second suspendible particle comprising a photosensitizer, wherein the second particle has bound thereto an sbp member. At least one of the sbp members is capable of binding to the analyte or to an sbp member complementary to the analyte. In another embodiment of this aspect, the kit comprises, in packaged combination, a photoactive indicator precursor containing a selenium or tellurium atom, wherein the photoactive indicator precursor is associated with a first sbp member; and a photosensitizer capable in its excited state of activating oxygen to its singlet state associated with a second sbp member. The sbp members are capable of binding to the analyte or to an sbp member capable of binding the analyte. Another aspect of this invention is a binding assay for an analyte that is an sbp member. The assay comprises the first step of combining a medium suspected of containing the analyte with an sbp member capable of binding directly or indirectly to the analyte or to an sbp member complementary to the analyte; a second step of detecting the binding of the sbp member to the analyte or the complementary sbp member, wherein the detection comprises exposing a photoactive indicator precursor in the medium to singlet oxygen to produce a photoactive indicator; and a final step of measuring the fluorescence of the photoactive indicator. Another aspect of this invention are compounds useful as photoactive indicator precursors which contain the following structure: wherein H is cis to the XR group; X is a selenium or tellurium; R is an organic or organometallic group bound to X through an unsaturated carbon atom, a silicon atom, or a tin atom; and A, when taken with the carbon- carbon group, forms an alicyclic ring (optionally fused to one or more aromatic rings) or a heterocyclic ring; where upon reaction of the compound with singlet oxygen, the H and the XR group are replaced by a carbon-carbon double bond to yield a fluorescent molecule having an extinction coefficient of at least 10,000 HT'cm "1 at its absorption maximum and a fluorescence emission quantum yield of at least 0.1. Another aspect of this invention is a method for preparing a photoactive indicator molecule. The method comprises reacting a compound of the invention (as described above) with singlet oxygen to yield a photoactive indicator having an extinction coefficient of at least 10,000 ir'cm" 1 at its absorption maximum and a fluorescence emission quantum yield of at least 0.1. One of the advantages of the present invention is the ability of the fluorescent photoactive indicator (which is produced from the reaction of the photoactive indicator precursor with singlet oxygen) to generate at least 10 5 times as many photons as the chemiluminescent compound used in the method described above in European Published Patent Application No. 0 515 194. This is because a single fluorescent photoactive indicator molecule can often be excited up to 10 5 times before it is destroyed. Thus, the fluorescent photoactive indicator molecule that is formed in the present invention can produce tens of thousands of photons on irradiation. Detection of this fluorescence can therefore provide a more sensitive assay. Moreover, measurement of the fluorescence of the photoactive indicator molecule in the present invention permits the use of a standard fluorometer whereas detection of the chemiluminescence produced on activation of the chemiluminescent compound in the previously described assay requires more specialized spectrometers. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graphic depiction of the results of DNA detection assays. The results of each assay are depicted by a different symbol. DETAILED DESCRIPTION OF THE INVENTION Definitions As used in this specification and appended claims, unless specified to the contrary, the following terms have the meaning indicated: "Alkyl" refers to a monovalent branched or unbranched radical derived from an aliphatic hydrocarbon by removal of one hydrogen atom; includes both lower alkyl and upper alkyl. "Lower alkyl" refers to an alkyl radical containing from 1 to 5 carbon atoms, e.g., methyl, ethyl, propyl, butyl, isopropyl, isobutyl, pentyl, isopentyl, and the like. "Upper alkyl" refers to an alkyl radical containing more than 6 carbon atoms, usually 6 to 20 carbon atoms, e.g. , hexyl, heptyl, octyl, and the like. "Alkylidene" refers to a divalent organic radical derived from an alkyl radical in which two hydrogen atoms are taken from the same carbon atom, e.g. , ethylidene, and the like. "Alkylene" refers to a divalent organic radical derived from an alkyl radical in which two hydrogen atoms are taken from different carbon atoms. "Alicyclic ring" refers to a cyclic hydrocarbon radical of 5 to 7 carbons in length which may be unsaturated or partially saturated. "Aryl" refers to an organic radical derived from an aromatic hydrocarbon by the removal of one atom and containing one or more aromatic rings, usually one to four aromatic rings, e.g., phenyl (from benzene), naphthyl (from naphthalene) , and the like. "Aralkyl" refers to an organic radical having an alkyl group to which is attached an aryl group, e.g. , benzyl, phenethyl, 3-phenylpropyl, 1-naphthylethyl, and the like. "Alkoxy" refers to a radical of the formula -0R_ where R, iε an alkyl group, e.g. , methoxy, ethoxy, and the like. "Aryloxy" refers to a radical of the formula -OR,, where R,, is an aryl group, e.g. , phenoxy, naphthoxy, and the like. "Aralkoxy" refers to a radical of the formula -0R C where R 0 is an aralkyl radical, e.g. , benzyloxy, 1-naphthylethoxy, and the like. "Alkylthio" refers to a radical of the formula -SR, where S, iε an alkyl group, e.g. , methylthio, ethylthio, and the like. "Arylthio" refers to a radical of the formula -SR,, where R-, is an aryl group, e.g. , phenylthio, naphthylthio, and the like. "Heterocyclic ring" refers to a stable mono-, bi- or tricyclic ring system which consists of carbon atoms and from one to three heteroatoms selected from the group consisting of nitrogen, oxygen and sulfur and which is either saturated or unsaturated, wherein the nitrogen, carbon or sulfur atoms may optionally be oxidized, and the nitrogen atom may optionally be quaternized, and includes any ring system in which any of the above-defined heterocyclic ring systems iε fused to a benzene ring. The heterocyclic ring system may be substituted at any heteroatom or carbon atom which resultε in the creation of a εtable structure. Examples of such heterocyclic ring systems include, but are not limited to, piperidine, piperazine, 2-oxopiperazine, 2-oxopiperidine, 2-oxopyrrolidine, 2-oxoazepine, azepine, pyrrole, 4-piperidone, pyrrolidine, pyrazole, pyrazolidine, imidazole, imidazoline, imidazolidine, pyridine, pyrazine, pyrimidine, pyridazine, oxazole, oxazolidine, indane, isoxazole, isoxazolidine, morpholine, thiazole, thiazolidine, isothiazole, quinuclidine, isothiazolidine, indole, isoindole, indoline, isoindoline, octahydroindole, octahydroisoindole, quinoline, isoquinoline, decahydroisoquinoline, benzimidazole, thiadiazole, dihydrobenzofuran, benzofuran, benzopyran, 1,4-benzopyrone, 1,2-benzopyrone, benzothiazole, benzoxazole, furan, tetrahydrofuran, pyran, tetrahydropyran, thiophene, benzothiophene, thiamorpholine, thiamorpholine εulfoxide, thiamorpholine sulfone, and oxadiazole. Preferred heterocyclic rings for the purposes of this invention are benzopyrones. "Substituted" refers to the condition wherein a hydrogen atom of a molecule has been replaced by another atom, which may be a single atom such as a halogen, etc. , or part of a group of atoms, such as an organic group. 11 Electron-donating group" refers to a substituent which, when bound to a molecule, is capable of polarizing the molecule such that the electron-donating group becomes electron poor and positively charged relative to another portion of the molecule, i . e. , has reduced electron density. Such groups may be, by way of illustration and not limitation, amines, ethers, thioethers, phosphines, hydroxy, oxyanions, mercaptans and their anions, εulfides, etc. "Organic group" refers to a substituent having from 1 to 50 atoms other than the requisite number of hydrogen atoms necessary to satisfy the valencies of the atoms in the radical. Generally, the predominant atom in such a group is carbon (C) but may also be oxygen (O) , nitrogen (N) , sulfur (S) , phosphorus (P) , wherein, if present, the O, N, S, or P atom may be bound to carbon or to one or more of each other or to hydrogen or to a metal atom to form various functional groups, εuch as carboxylic acids, alcohols, thiolε, carboxamideε, carbamateε, carboxylic acid eεterε, sulfonic acidε, εulfonic acid esters, phosphoric acids, phosphoric acid esterε, ureaε, carbamateε, phosphoramides, sulfonamides, ethers, sulfides, thioethers, olefins, acetylenes, amines, ketones, aldehydes, nitriles, and the like. Illustrative of such organic groups, by way of illustration and not limitation, are alkyl, alkylidine, aryl, aralkyl, and heterocyclyl, wherein the alkyl, alkylidine, aryl, aralkyl or heterocyclyl group may be substituted with one or more of the aforementioned functional groups. "Organometallic group" refers to a radical containing an organic group (as defined above) linked to a metal atom. "Analyte" refers to the compound or composition to be detected. The analyte can be comprised of a member of a specific binding pair (sbp) and may be a ligand, which is monovalent (monoepitopic) or polyvalent (polyepitopic) , usually antigenic or haptenic, and is a single compound or plurality of compounds which share at least one common epitopic or determinant site. The analyte can be a part of a cell such as bacteria or a cell bearing a blood group antigen εuch aε A, B, D, etc. , or an HLA antigen or a microorganism, e.g. , bacterium, fungus, protozoan, or viruε. The polyvalent ligand analytes will normally be poly(amino acids) , i.e., polypeptides and proteins, polyεaccharides, nucleic acids, and combinations thereof. Such combinations include components of bacteria, viruεes, chromosomeε, genes, mitochondria, nuclei, cell membranes and the like. For the most part, the polyepitopic ligand analytes to which the subject invention can be applied will have a molecular weight of at least about 5,000, more uεually at leaεt about 10,000. In the poly(amino acid) category, the poly(amino acids) of interest will generally be from about 5,000 to 5,000,000 molecular weight, more usually from about 20,000 to 1,000,000 molecular weight; among the hormones of interest, the molecular weights will uεually range from about 5,000 to 60,000 molecular weight. A wide variety of proteinε may be considered aε to the family of proteins having similar structural features, proteins having particular biological functions, proteins related to specific microorganiεmε, particularly diεease causing microorganiεmε, etc. Such proteinε include, for example, immunoglobulinε, cytokines, enzymes, hormones, cancer antigens, nutritional markers, tisεue specific antigens, etc. The types of proteins, blood clotting factors, protein hormones, antigenic polysaccharideε, microorganisms and other pathogens of interest in the preεent invention are specifically disclosed in U.S. Patent No. 4,650,770, the disclosure of which is incorporated by reference herein in its entirety. The monoepitopic ligand analytes will generally be from about 100 to 2,000 molecular weight, more usually from 125 to 1,000 molecular weight. The analytes include drugs, metabolites, pesticides, pollutants, and the like. Included among drugs of interest are the alkaloids. Among the alkaloids are morphine alkaloidε, which includes morphine, codeine, heroin, dextromethorphan, their derivatives and metabolites; cocaine alkaloids, which include cocaine and benzyl ecgonine, their derivatives and metabolites; ergot alkaloids, which include the diethylamide of lysergic acid; steroid alkaloids; iminazoyl alkaloids; quinazoline alkaloids; iεoquinoline alkaloidε; quinoline alkaloidε, which include quinine and quinidine; diterpene alkaloids, their derivatives and metabolites. The next group of drugs includes εteroidε, which includeε the eεtrogens, androgens, adrenocortical steroids, bile acids, cardiotonic glycosideε and aglycones, which includes digoxin and digoxigenin, saponins and sapogenins, their derivatives and metabolites. Also included are the steroid mimetic substanceε, such as diethylstilbestrol. The next group of drugε iε lactamε having from 5 to 6 annular memberε, which include the barbiturateε, e.g. , phenobarbital and secobarbital, diphenylhydantoin, primidone, ethosuximide, and their metabolites. The next group of drugε iε aminoalkylbenzeneε, with alkyl of from 2 to 3 carbon atoms, which includes the amphetamines; catecholamines, which includeε ephedrine, L-dopa, epinephrine; narceine; papaverine; and metaboliteε of the above. The next group of drugs is benzheterocyclics which include oxazepam, chlorpromazine, tegretol, their derivatives and metabolites, the heterocyclic rings being azepineε, diazepineε and phenothiazineε. The next group of drugε is purines, which includes theophylline, caffeine, their metabolites and derivativeε. The next group of drugε includeε thoεe derived from marijuana, which includes cannabinol and tetrahydrocannabinol. The next group of drugs is the hormones such as thyroxine, cortisol, triiodothyronine, teεtosterone, estradiol, estrone, progesterone, polypeptides such as angiotensin, LHRH, and immunosuppressants such as cyclosporin, FK506, mycophenolic acid, and so forth. The next group of drugs includes the vitamins such as A, B (e.g. , B 12 ) , C, D, E and K, folic acid, thiamine. The next group of drugs is prostaglandins, which differ by the degree and siteε of hydroxylation and unεaturation. The next group of drugs is the tricyclic antidepreεεants, which include imipramine, dismethylimipramine, amitriptyline, nortriptyline, protriptyline, trimipramine, chlomipramine, doxepine, and desmethyldoxepin, The next group of drugs are the anti-neoplasties, which include methotrexate. The next group of drugs is antibiotics, which include penicillin, chloromycetin, actinomycetin, tetracycline, terramycin, the metabolites and derivatives. The next group of drugs iε the nucleosides and nucleotides, which include ATP, NAD, FMN, adenoεine, guanoεine, thymidine, and cytidine with their appropriate sugar and phosphate substituents. The next group of drugε iε miεcellaneous individual drugε which include methadone, meprobamate, serotonin, meperidine, lidocaine, procainamide, acetylprocainamide, propranolol, griseofulvin, valproic acid, butyrophenoneε, antihistamines, chloraπrphenicol, anticholinergic drugs, such aε atropine, their metabolites and derivatives. Metabolites related to diseased states include εpermine, galactose, phenylpyruvic acid, and porphyrin Type 1. The next group of drugε iε aminoglycoεideε, εuch aε gentamicin, kanamycin, tobramycin, and amikacin. Among pesticides of interest are polyhalogenated biphenyls, phoεphate eεterε, thiophosphates, carbamateε, polyhalogenated εulfenamideε, their metaboliteε and derivatives. For receptor analytes, the molecular weights will generally range from 10,000 to 2xl0 8 , more usually from 10,000 to 10*. For immunoglobulins, IgA, IgG, IgE and IgM, the molecular weightε will generally vary from about 160,000 to about 10*. Enzymeε will normally range from about 10,000 to 1,000,000 in molecular weight. Natural receptorε vary widely, generally being at leaεt about 25,000 molecular weight and may be 10 6 or higher molecular weight, including such materials as avidin, εtreptavidin, DNA, RNA, thyroxine binding globulin, thyroxine binding prealbumin, tranεcortin, etc. The term einalyte further includes polynucleotide analytes such aε thoεe polynucleotides defined below. These include m-RNA, r-RNA, t-RNA, DNA, DNA-RNA duplexes, etc. The term einalyte also includeε receptors that are polynucleotide binding agents, such as, for example, restriction enzymeε, activators, repressors, nucleases, polymeraεeε, histones, repair enzymes, chemotherapeutic agents, and the like. The einalyte may be a molecule found directly in a εample εuch aε a body fluid from a hoεt. The εample can be examined directly or may be pretreated to render the analyte more readily detectible. Furthermore, the analyte of intereεt may be determined by detecting an agent probative of the analyte of intereεt εuch aε a specific binding pair member complementary to the analyte of interest, whose presence will be detected only when the analyte of intereεt iε present in a sample. Thus, the agent probative of the analyte becomes the analyte that is detected in an assay. The body fluid can be, for example, urine, blood, plasma, serum, saliva, semen, stool, sputum, cerebral spinal fluid, tears, mucus, and the like. "Specific binding pair (sbp) member" refers to one of two different molecules, having an area on the surface or in a cavity which specifically binds to and is thereby defined as complementary with a particular spatial and polar organization of the other molecule. The members of the specific binding pair are referred to as ligand and receptor (antiligand) . These will usually be memberε of an immunological pair εuch as antigen-antibody, although other specific binding pairε εuch aε biotin-avidin, hormoneε-hormone receptors, nucleic acid duplexes, IgG-protein A, polynucleotide pairs such as DNA-DNA, DNA-RNA, and the like are not immunological pairs but are included in the invention and the definition of sbp member. "Polynucleotide" refers to a compound or composition which iε a polymeric nucleotide having in the natural εtate about 6 to 500,000 or more nucleotideε and having in the iεolated εtate about 6 to 50,000 or more nucleotideε, uεually about 6 to 20,000 nucleotideε, more frequently 6 to 10,000 nucleotideε. The term "polynucleotide" alεo includeε oligonucleotides and nucleic acids from any source in purified or unpurified form, naturally occurring or synthetically produced, including DNA (dsDNA and ssDNA) and RNA, usually DNA, and may be t-RNA, m-RNA, r-RNA, mitochondrial DNA and RNA, chloroplast DNA and RNA, DNA-RNA hybrids, or mixtures thereof, genes, chromosomes, plasmids, the genomes of biological material such as microorganisms, e.g. , bacteria, yeasts, viruses, viroids, moldε, fungi, plantε, animals, humans, and fragments thereof, and the like. "Polynucleotide probe" refers to single-stranded nucleic acid molecules having base sequences complementary to that of the target polynucleotide analyte. Probes will generally consist of chemically or synthesized DNA or RNA polynucleotides from 6 to 200 base pair in length and must be capable of forming a stable hybridization complex with the target polynucleotide analyte. "Ligand" refers to any organic compound for which a receptor naturally exists or can be prepared. The term ligand also includes ligand analogs, which are modified ligands, usually an organic radical or analyte analog, usually of a molecular weight greater than 100, which can compete with the analogous ligand for a receptor, the modification providing means to join the ligand analog to another molecule. The ligand analog will usually differ from the ligand by more than replacement of a hydrogen with a bond which links the ligand analog to a hub or label, but need not. The ligand analog can bind to the receptor in a manner similar to the ligand. The analog could be, for example, an antibody directed against the idiotype of an antibody to the ligand. "Receptor" or "antiligand" refers to any compound or composition capable of recognizing a particular spatial and polar organization of a molecule, e.g. , epitopic or determinant site. Illustrative receptors include naturally occurring receptors, e.g. , thyroxine binding globulin, antibodies, enzymes, Fab fragments, lectins, nucleic acids, avidin, protein A, barstar, complement component Clq, and the like. Avidin is intended to include egg white avidin and biotin binding proteins from other sources, such aε streptavidin. "Specific binding" referε to the specific recognition of one of two different molecules for the other compared to subεtantially leεε recognition of other moleculeε. Generally, the molecules have areas on their surfaces or in cavities giving rise to specific recognition between the two molecules. Exemplary of specific binding are antibody-antigen interactions, enzyme-substrate interactions, polynucleotide interactions, and εo forth. "Non-specific binding" refers to the non-covalent binding between molecules that is relatively independent of specific surface structures. Non-specific binding may result from several factors including hydrophobic interactions between moleculeε. "Antibody" refers to an immunoglobulin which specifically binds to and iε thereby defined aε complementary with a particular spatial and polar organization of another molecule. The antibody can be monoclonal or polyclonal and can be prepared by techniques that are well known in the art such as immunization of a host and collection of sera (polyclonal) or by preparing continuous hybrid cell lines and collecting the secreted protein (monoclonal) , or by cloning and expressing nucleotide sequences or mutagenized versions thereof coding at least for the amino acid sequences required for specific binding of natural antibodies. Antibodies may include a complete immunoglobulin or fragment thereof, which immunoglobulins include the various classeε and iεotypeε, εuch aε IgA, IgD, IgE, IgGl, IgG2a, IgG2b and IgG3, IgM, etc. Fragmentε thereof may include Fab, Fv and F(ab') 2 , Fab', and the like. In addition, aggregates, polymers, and conjugates of immunoglobulins or their fragments can be used where appropriate so long as binding affinity for a particular molecule is maintained. "Linking group" refers to the covalent linkage between molecules. The linking group will vary depending upon the nature of the molecules, such as a photoεensitizer, a photoactive indicator precursor, an sbp member or the molecule asεociated with or part of a particle, being linked. Functional groupε that are normally present or are introduced on a photosensitizer or a photoactive indicator precursor will be employed for linking these molecules to an sbp member or to a particle εuch aε a lipophilic component of a liposome or oil droplet, latex particle, silicon particle, metal εol, or dye cryεtallite. For the most part, carbonyl functionalities are useful as linking groupε, such as oxocarbonyl groups such as aldehydes, acetyl and carboxy groupε; and non-oxocarbonyl groups (including nitrogen and sulfur analogε) εuch aε amidine, amidate, thiocarboxy and thionocarboxy. Alternative functionalitieε of oxo are alεo useful as linking groupε, εuch as halogen, diazo, mercapto, olefin (particularly activated olefin) , amino, phoεphoro and the like. A good description of linking groups may be found in U.S. Patent No. 3,817,837, which disclosure is incorporated herein by reference. The linking groups may vary from a bond to a chain of from 1 to 100 atoms, usually from about 1 to 70 atoms, preferably 1 to 50 atoms, more preferably 1 to 20 atoms, each independently selected from the group normally conεiεting of carbon, oxygen, εulfur, nitrogen and phoεphorouε. The number of heteroatomε in the linking groups will normally range from about 0 to 20, usually from about 1 to 15, more preferably 2 to 6. The atomε in the chain may be substituted with atoms other than hydrogen in a manner similar to that described for organic groups. As a general rule, the length of a particular linking group can be selected arbitrarily to provide for convenience of synthesis, minimize interference of binding sbp members, and permit the incorporation of any desired group such as a fluorescent energy acceptor, or a catalyst of intersyεtem croεεing εuch aε a heavy atom, and the like. The linking groups may be aliphatic or aromatic, although with diazo groups, aromatic groups will uεually be involved. When heteroatoms are present, oxygen will normally be present as oxo or oxy, bonded to carbon, sulfur, nitrogen or phosphorous; nitrogen will normally be present as nitro, nitroso or amino, normally bonded to carbon, oxygen, εulfur or phoεphorous; sulfur would be analogous to oxygen; while phosphorouε will be bonded to carbon, εulfur, oxygen or nitrogen, uεually as phosphonate and phoεphate mono- or dieεter. Common functionalitieε in forming a covalent bond between the linking group and the molecule to be conjugated are alkylamine, amidine, thioamide, ether, urea, thiourea, guanidine, azo, thioether and carboxylate, εulfonate, and phosphate eεterε, amides and thioesters. For the most part, where the photosenεitizer and the photoactive indicator precursor of the present invention are linked to a particle, εurface or εbp member, they will have a non-oxocarbonyl group (including nitrogen and sulfur analogs) , a phosphate group, an amino group, an alkylating agent (e.g. , such as halo or toεylalkyl) , an ether group (including hydroxy) , a thioether group (including mercapto) , an oxocarbonyl group (e.g. , aldehyde or ketone) , or an active olefin εuch aε a vinyl sulfone or an a,β-unsaturated ester or amide. These functionalities will be linked to a particle, surface or an sbp member having functionalitieε such as amine groups, carboxyl groups, active olefins, or alkylating agents, e.g. , bromoacetyl. Where an amine and carboxylic acid or itε nitrogen derivative or phosphoric acid are linked, amides, amidines and phosphoramides will be formed. Where mercaptan and activated olefin are linked, thioethers will be formed. Where a mercaptan and an alkylating agent are linked, thioethers will be formed. Where aldehyde and an amine are linked under reducing conditions, an alkylamine will be formed. Where a carboxylic acid or phosphate acid and an alcohol are linked, esters will be formed. "A group or functionality imparting hydrophilicity or water solubility" refers to a hydrophilic functionality, which increaseε wettability of εolidε with water and the solubility in water of compounds to which it iε bound. Such a functional group or functionality can be an organic group and can include a sulfonate, sulfate, phoεphate, amidine, phosphonate, carboxylate, hydroxyl particularly polyols, amine, ether, amide, and the like. Illuεtrative functional groupε are carboxyalkyl, sulfonoxyalkyl, CONHOCH 2 COOH, CO- (glucosamine) , sugars, dextran, cyclodextrin, SOjNHCH-jCOOH, S0 3 H, CONHCH 2 CH 2 S0 3 H, P0 3 H 2 , OP0 3 H 2 , hydroxyl, carboxyl, ketone, and combinations thereof. Most of the above functionalities can alεo be utilized as attaching groups, which permit attachment of the photosensitizer or photoactive indicator precurεor to an εbp member or a support. "A group or functionality imparting lipophilicity or lipid εolubility" iε a lipophilic functionality, which decreaεeε the wettability of surfaces by water and the solubility in water of compounds to which it is bound. Such a functional group or functionality can contain 1 to 50 or more atoms, usually carbon atoms subεtituted with hydrogen or halogen and can include alkyl, alkylidene, aryl and aralkyl. The lipophilic group or functionality will normally have one to six straight or branched chain aliphatic groups of at least 6 carbon atoms, more usually at least 10 carbon atoms, and preferably at least 12 carbon atomε, usually not more than 30 carbon atomε. The aliphatic group may be bonded to rings of from 5 to 6 members, which may be alicyclic, heterocyclic, or aromatic. "Photosenεitizer" refers to a molecule which, for the purposeε of this invention, can be excited to a metastable state, usually a triplet state, which in the proximity of molecular oxygen can directly or indirectly transfer its energy to the oxygen with concomitant excitation of the oxygen to a highly reactive excited state of oxygen often referred to aε singlet oxygen or O 2 ('Δ g ) . The photosensitizer will usually be excited by the abεorption of light or by an energy tranεfer from an excited state of a suitable donor but may also be excited by chemiexcitation, electrochemical activation or by other means. Usually excitation of the photosensitizer will be caused by irradiation with light from an external source. The photosensitizerε of this invention will usually have an absorption maximum in the wavelength range of 250 to 1100 nm, preferably 300 to 1000 nm, and more preferably 450 to 950 nm, with an extinction coefficient at its absorbance maximum greater than 500 M ^ 'crn "1 , preferably at least 5000 w'cm' 1 , more preferably at least 50,000 M '1 cm "1 . The lifetime of the excited state, usually a triplet state, produced following absorption of light by the photosensitizer will usually be at least 100 nsec, preferably at least 1 μsec in the absence of oxygen. In general, the lifetime muεt be εufficiently long to permit the energy tranεfer to oxygen, which will normally be preεent at concentrations in the range of 10" 5 to 10 _3 M (depending on the medium) . The excited state of the photosensitizer will usually have a different spin quantum number (S) than its ground state and will usually be in a triplet (S=l) εtate when, aε is usually the case, the ground state iε a εinglet (S=0) . Preferably, the photoεenεitizer will have a high interεystem crosεing yield. That iε, excitation of a photosensitizer will produce the long lived state (usually triplet) with an efficiency of at least 10%, desirably at least 40%, preferably greater than 80%. The photosenεitizer will usually be at most weakly fluorescent under the asεay conditionε (quantum yield usually leεε than 0.5, preferably leεε that 0.1) . Photoεensitizers of the instant invention are relatively photostable and will not react efficiently with the singlet molecular oxygen so generated. Several structural features are present in most uεeful photoεenεitizerε. Most photosenεitizers have at least one and frequently three or more conjugated double or triple bondε held in a rigid, frequently aromatic εtructure. They will frequently contain at least one group that accelerates interεystem crosεing such as a carbonyl or imine group or a heavy atom selected from rows 3 through 6 of the periodic table, eεpecially iodine or bromine, or they will frequently have polyaromatic εtructures. Typical photosensitizerε include ketoneε εuch as acetone, benzophenone and 9-thioxanthone; xanthenes such aε eosin and rose bengal; polyaromatic compounds such as buckminsterfullerene and 9,10-dibromoanthracene; porphyrinε including metallo-porphyrins εuch as hematoporphyrin and chlorophylls; oxazines; cyanines; εquarate dyes; phthalocyanineε; merocyanines; thiazines εuch as methylene blue, etc., and derivatives of these compounds substituted by an organic group for enhancing intersyεtem crossing and rendering such compounds more lipophilic or more hydrophilic and/or aε attaching groupε for attachment, for example, to an εbp member. Exampleε of other photosensitizers that may be utilized in the present invention are thoεe that have the above propertieε and are enumerated in N.J. Turro, "Molecular Photochemistry", page 132, W.A. Benjamin Inc., N.Y. 1965. The photosenεitizerε of the inεtant invention are preferably relatively non-polar to aεsure dissolution into a lipophilic member when the photosenεitizer is incorporated into a suspendible particle such as an oil droplet, liposome, latex particle, and the like. "Photoactive indicator precursor" refers to those molecules which react with singlet oxygen to form photoactive indicators or to form a compound that can react with an auxiliary compound that is thereupon converted to a photoactive indicator. There are several types of reactions of singlet oxygen that can give compoundε that will lead to a photoactive indicator compound. The type of reaction that iε employed and the choice of the photoactive indicator that is desired provides a guide to the structures of the photoactive indicator precursors and any auxiliary compounds used in the preεent invention. The photoactive indicator precurεor will preferably undergo a reaction with singlet oxygen that is very rapid, usually at leaεt 10 4 to 10 6 sec "1 , preferably at least 10 6 to 10 s sec "1 , more preferably >10 8 sec" 1 . When the initial product of the reaction is an intermediate that reacts to give the photoactive precursor, the intermediate will preferably have a lifetime that is εhort relative to the deεired time between forming singlet oxygen and detecting the fluorescence emitted from the photoactive indicator upon exposure to light. For simultaneous singlet oxygen generation and fluoreεcence detection the lifetime will usually be 10 "3 to 10 sec, preferably 10" 3 sec. When generation of singlet oxygen and fluorescence detection are sequential the lifetime may vary from 10" 3 εec to 30 minuteε or more, preferably <1 sec to 60 sec. Higher rates of reaction of singlet oxygen are achieved by providing singlet oxygen reactive groups in the photoactive indicator precursor that are electron rich. These groups will usually be an olefin or acetylene, hydrazine and hydroxylamine derivatives, selenides and tellurides but are not limited to these groupε. For example, tellurides have been found to be particularly useful because they react rapidly with singlet oxygen to produce an olefin. The reaction rate depends on the electron availability (oxidation potential) of the tellurium. For example, electron donating groups on an aryl ring substituent on the tellurium atom can increase the rate. Changing from tellurium to selenium (the next lower chalcogenide) will decrease the rate, but increase the oxidation stability of the molecule. When the photoactive indicator precurεor contains a hydrazine or hydrazide, reaction with singlet oxygen can produce a double bond. For example, singlet oxygen can convert hydrazides directly into fluoreεcent photoactive indicators, as illustrated in the following reaction: The oxidation potential of a hydrazine is an important factor in providing a high rate of reaction. Electron withdrawing groups such as an acyl group (e.g. , as in a hydrazide) εlow the reaction although acyl hydrazides and diacyl hydrazides can still be used as photoactive indicator precursors in the present invention. When the reaction is insufficiently rapid it can often be accelerated in the presence of a base. For example, 3-aminophthaloyl hydrazide forms an anion in the presence of strong base that is electron rich and can react rapidly with singlet oxygen to form 3-aminophthalate as the photoactive indicator. However, the hydroxyl ion cannot be used aε a base when the suspendible particles contain the photoactive indicator precurεor within a hydrophobic matrix. Hydrophilic particleε εuch aε agaroεe can be used instead to permit accesε to the hydroxyl ion. Usually the photoactive indicator precurεor will be covalently bound to the εuεpendible particle when the particle iε hydrophilic. Still another example of a uεeful εinglet oxygen reaction is the reaction with electron rich olefins such as those described in European Published Patent Application No. 0 515 194. Two fundamental types of reactions are described. One of these iε the "ene" reaction which iε exemplified by the following transformation: This reaction εhiftε the position of a double bond and produces a hydroperoxide. The double bond shift can cause two auxochromic groups in the photoactive indicator precursor to come into conjugation and thus produce a fluorescent photoactive indicator. Other photoactive indicator precursors react with singlet oxygen to form hydroperoxides which can react internally with an oxidizable group to give a fluoreεcent photoactive indicator. An example of εuch a precurεor and the εubεequent reaction and product include the following: Alternatively, a hydroperoxide formed by reaction of singlet oxygen with a photoactive indicator precursor, such as 1,3-diphenylpropene, can serve to oxidize the leuco form of a dye which is present as an auxiliary compound so as to form a fluorescent photoactive indicator. The hydroperoxide can also oxygenate a group V element in an auxiliary compound to cause it to act aε an electron donating quencher of an associated fluorescent group. For example, the auxiliary compound: which iε poorly fluoreεcent, can be oxygenated by a hydroperoxide to give the more highly fluorescent compound: The auxiliary compound could alternatively have a selenium or tellurium atom that could react with a hydroperoxide to produce an intermediate that could undergo subεequent elimination to form a fluorescent photoactive indicator. Alternatively, the photoactive indicator precursor will react εlowly or not at all with εinglet oxygen but will react with a hydroperoxide reaction product of singlet oxygen and an auxiliary molecule. For example, in the following reaction, the auxiliary compound is reacted with singlet oxygen to form a hydroperoxide, which iε then reacted with the photoactive indicator precurεor of formula (Ik) to form a fluoreεcent photoactive indicator: ( ■ ) (b) (Ik) In each of theεe exampleε the auxiliary compound and the photoactive indicator precurεor may be covalently linked. In such an occurrence, the resulting molecule is referred to as a photoactive indicator precurεor. The second typical reaction of olefins with singlet oxygen is 2 + 2 addition to form a dioxetane. This reaction can lead to bond breaking and therefore can separate a quenching group from a fundamentally fluorescent molecule. Alternatively the bond breaking step can lead to a ketone, aldehyde or eεter which could be fluorescent or which could undergo subsequent reactions that could lead to a fluoreεcent molecule. In all of the above olefin reactionε the rate will be faster if the olefin is εubεtituted with electron donating groups such aε etherε, thioetherε, amineε, and the like. Still another type of reaction of εinglet oxygen is 4 + 2 cycloadditions with dieneε. Such reactions lead initially to endoperoxideε. In some caseε endoperoxideε can rearrange to active eεterε or anhydrideε that are capable of reaction with a εuitably placed group to provide a lactone or lactam that can be fluorescent. For example, the endoperoxide formed in the following reaction scheme can rearrange to form a fluorescent lactone: Alternatively, the endoperoxides may oxidize a photoactive indicator precursor much as described above for hydroperoxideε. Additional examples of photoactive indicator precursors' reaction with singlet oxygen to produce fluorescent photoactive indicator molecules are illustrated below: The structure of the photoactive indicator precurεor will therefore depend on the particular εinglet oxygen reaction that iε to be employed and it will usually be designed to asεure that any subsequent reactions initiated by reaction with singlet oxygen that are required to produce a photoactive indicator will proceed relatively rapidly. Additionally the structure of the photoactive indicator precursor will lead to the formation of a photoactive indicator that has the desired absorption and emission wavelengthε, and haε relatively high fluoreεcent quantum yieldε, preferably >0.1, more preferably greater than 0.4, and a high extinction coefficient at the desired excitation wavelength, preferably >1000 M" 1 cm" 1 , more preferably >10,000 M" 1 cm "1 . Preferred photoactive indicator precursors of the present invention include compounds containing the following structure (I) : wherein H is cis to the XR group; X is a εelenium or tellurium atom; R iε an organic or organometallic group bound to X through an unsaturated carbon atom, a silicon atom, or a tin atom; and A, when taken with the carbon- carbon group, forms an alicyclic ring (optionally fused to one or more aromatic rings) or a heterocyclic ring; where, upon reaction of the compound with singlet oxygen, the H and the XR groupε are replaced by a carbon-carbon double bond to yield a fluoreεcent molecule having an extinction coefficient of at leaεt 10,000 M '1 cm "1 at its absorption maximum and a fluorescence quantum efficiency of at least 10%. Particularly preferred within these compounds are those compounds wherein X is tellurium. Most preferred is the compound of the following formula: wherein R iε an organic or organometallic group bound to X through an unsaturated carbon atom, a silicon atom, or a tin atom; and R 1 is hydrogen or alkyl; and wherein up to four of the remaining hydrogen atoms may be replaced by alkyl or alkylene substituents which may be taken together to form one or more alicyclic or aromatic rings. The compounds disclosed herein containing structure (I) are designated herein aε derivativeε of the structure, e.g. , compound of formula (la) , compound of formula (If) or compound of formula (Ik) . Examples of εuch compounds where X is tellurium and the fluoreεcent photoactive indicator molecule formed upon the compoundε' reaction with εinglet oxygen are given below: ( la) ( lb) & ( le) ( Id) (i (ii) (U. Preεently, preferred photoεenεitive indicator precurεorε of the invention are the compounds of formula (Ie) and (If) above. The phenyltelluridyl radical (-TeC^) in these compoundε can be replaced with other tellurium derivativeε, εuch aε TeSiC(CH 3 ) 3 and TeSn( (CH 2 ) 3 CH 3 ) 3 , or the phenyl group can be εubstituted, preferably with electron donating groups such aε -N(CH 3 ) 2 and -OCH 3 . When X iε εelenium it iε preferable that the εelenium iε substituted by a strong electron donor group or atom, such as tin. Other classes of photoactive indicator precursors can also be used in the present invention. For example, compoundε that chemilumineεce on reaction with εinglet oxygen are frequently converted to fluoreεcent products which can εerve aε photoactive indicatorε of the preεent invention. Exampleε of εuch photoactive indicator precurεors and the photoactive indicators produced upon reaction with singlet oxygen include the following: an d 11 Photoactive indicator" refers to a molecule which, following absorption of light of wavelengths of 250 to 1100 nm, preferably 300 to 950 nm, emits light by fluorescence or phosphorescence, preferably by fluorescence, or transfers it excitation energy to an acceptor molecule which thereupon emits light by fluorescence or phosphorescence. Preferably the emission quantum yield will be high, usually at leaεt 0.1, preferably at leaεt 0.4, more preferably greater than 0.7 and the extinction coefficient of the abεorption maximum will usually be greater than 5000 M "1 cm" 1 . Photoactive indicators of this invention are typically fluorescent compounds, such as fluorescent brighteners, which typically abεorb light between 300 and 400 nanometers and emit between 400 and 500 nanometers; xanthenes such aε rhodamine and fluorescein; bimanes; coumarins εuch aε umbelliferone; aromatic amines such aε dansyl; squarate dyes; benzofurans; cyanineε, merocyanineε, rare earth chelates, and the like. Photoactive indicators that are phosphorescent include porphyrins, phthalocyanines, polyaromatic compounds such as pyrene, anthracene and acenaphthene. Photoactive indicators alεo include chromenes. Photoactive indicators that can transfer energy to an acceptor molecule will usually absorb at 250 to 550 nm. Such acceptor molecules are luminescent and can include any of the above mentioned fluorescent and phosphorescent photoactive indicators. "Measuring the fluorescence" referε to the detection and calculation of the amount of light emitted from a photoactive indicator of the invention upon excitation by irradiation with light. While the fluorescence of the photoactive indicator will usually be measured by exciting the photoactive indicator by irradiation with light and simultaneouεly detecting the light that iε emitted therefrom (i.e., the fluoreεcence) , other methods of detecting the fluorescence are contemplated by this invention. The measurement of fluorescence iε intended to include detection of light emitted by the photoactive indicator simultaneous with or immediately following irradiation with light regardless of whether the light is absorbed directly or indirectly or whether the emisεion is from an excited εinglet εtate or state of higher multiplicity. Measurement of fluoreεcence is also intended to include the measurement of light emitted from the photoactive indicator following transfer of energy from a donor that is excited through chemiexcitation other than chemiexcitation initiated by absorption of light by the photosensitizer. For example, measurement of fluoreεcence of the photoactive indicator includeε activation of a chemilumineεcent molecule, for example, by addition of hydrogen peroxide and peroxidase to luminol, and measurement of the light emitted from the photoactive indicator aε a result of the energy transfer from the luminol reaction product to the photoactive indicator. "Support" or "surface" refers to a surface comprised of a porous or non-porous water insoluble material. The surface can have any one of a number of shapeε, such as strip, rod, particle, including bead, and the like. The surface can be hydrophilic or capable of being rendered hydrophilic and includes inorganic powders such as silica, magnesium sulfate, and alumina; natural polymeric materials, particularly cellulosic materialε and materials derived from cellulose, εuch aε fiber containing papers, e.g. , filter paper, chromatographic paper, etc. ; synthetic or modified naturally occurring polymers, such as nitrocellulose, cellulose acetate, poly (vinyl chloride) , polyacrylamide, crosε linked dextran, agarose, polyacrylate, polyethylene, polypropylene, poly(4-methylbutene) , polystyrene, polymethacrylate, poly(ethylene terephthalate) , nylon, poly(vinyl butyrate) , etc.; either used by themselveε or in conjunction with other materialε; glaεs available as Bioglaεε, ceramics, metals, and the like. Natural or synthetic asεemblies such as lipoεomeε, lipid veεicleε, and cellε can also be employed. Binding of sbp members to the support or surface may be accomplished by well-known techniques, commonly available in the literature. See, for example, "Immobilized Enzymes," Ichiro Chibata, Halsted Preεε, New York (1978) and Cuatrecaεas, J. Biol . Chem. , 245:3059 (1970). The surface will usually be polyfunctional or be capable of being polyfunctionalized or be capable of binding a polynucleotide, an sbp member, a photosensitizer, and/or a photoactive chemiluminescent compound through εpecific or non-specific covalent or non-covalent interactions. A wide variety of functional groups are available or can be incorporated. Functional groups include carboxylic acids, aldehydes, amino groupε, cyano groups, ethylene groups, hydroxyl groups, mercapto groups and the like. The manner of linking a wide variety of compounds to surfaces is well known and is amply illustrated in the literature. See for example Cautrecasas, J. Biol . Chem. 245.3059 (1970) . The length of a linking group to the oligonucleotide or εbp member may vary widely, depending upon the nature of the compound being linked, the effect of the distance between the compound being linked and the surface on the specific binding properties and the like. "Suspendible particles" refers to particles capable of being able to be εuεpended in water which are at least about 20 nm and not more than about 20 microns, usually at least about 40 nm and lesε than about 10 micronε, preferably from about 0.10 to 2.0 micronε in diameter, and which normally have a volume of leεε than about 4 picoliterε. The εuεpendible particleε may be organic or inorganic, swellable or non-swellable, porous or non-porous, preferably of a density approximating water (generally from about 0.7 to about 1.5g/ml), and composed of material that can be tranεparent, partially transparent, or opaque. The suspendible particles will usually be charged, preferably negatively charged. The suspendible particles may be solid (e.g. , polymer, metal, glaεε, organic and inorganic εuch aε minerals, salts and diatoms), oil droplets (e.g., hydrocarbon, fluorocarbon, εilicon fluid), or veεicleε (e.g. , synthetic such as phospholipid or other lipidε εuch aε dialkyl phoεphateε or natural εuch as cells and organelleε) . The suεpendible particleε may be latex particleε or other particleε compriεed of organic or inorganic polymerε; lipid veεicleε, e.g. , lipoεomeε; phoεpholipid vesicles; oil droplets; εilicon particles; metal sols; cells; and dye crystallite . If organic, the suspendible particles may be polymers, either addition or condensation polymers, which are readily suspendible in the assay medium. The organic εuεpendible particleε will alεo be adεorptive or functionalizable so aε to bind at their surface an sbp member (either directly or indirectly) and to bind at their surface or incorporate within their volume a photosensitizer or a photoactive indicator precurεor. The suspendible particleε can be derived from naturally occurring materialε, naturally occurring materials which are synthetically modified and synthetic materialε. Natural or synthetic asεemblieε εuch aε lipid bilayerε, e.g. , lipoεomeε and non-phoεpholipid veεicleε, are preferred. Among organic polymerε of particular interest are polysaccharides, particularly croεε-linked polyεaccharideε, such as agarose, which iε available aε Sepharoεe, dextran, available aε Sephadex and Sephacryl, celluloεe, starch, and the like; addition polymers, such aε polyεtyrene, polyacrylamide, homopolymerε and copolymerε of derivatives of acrylate and methacrylate, particularly esters and amides having free hydroxyl functionalitieε including hydrogels, and the like. Inorganic polymers include silicones, glasseε, available as Bioglas, and the like. Solε include gold, εelenium, and other metals. Suspendible particles may also be dispersed water insoluble dyes such as porphyrins, phthalocyanineε, etc. , which may also act aε photoεensitizers. Suεpendible particleε may alεo include diatomε, cellε, viral particleε, oil dropletε, fat particleε such as alkyl triglycerides, magnetosomes, cell nuclei and the like. Where non-polymeric particleε are uεed, the particle εize may be varied by breaking larger particles into smaller particles by mechanical means, such as grinding, εonication, agitation, etc. Like the εurface or support defined above, the suspendible particles will usually be polyfunctional or be capable of being polyfunctionalized or be capable of being bound to an sbp member, photosenεitizer, or photoactive indicator precurεor through specific or non-specific covalent or non-covalent interactions. A wide variety of functional groupε are available or can be incorporated. Exemplary functional groups include carboxylic acids, aldehydes, amino groups, cyano groups, ethylene groupε, hydroxyl groupε, mercapto groupε and the like. When covalent attachment of an εbp member, chemilumineεcent compound or photosensitizer to the particle is employed, the manner of linking is well known and iε amply illustrated in the literature. See for example Cautrecasaε, J. Biol . Chem. , 245:3059 (1970) . The length of a linking group may vary widely, depending upon the nature of the compound being linked, the nature of the particle, the effect of the diεtance between the compound being linked and the particle on the binding of sbp members and the analyte and the like. The photoεensitizer and/or photoactive indicator precursor can be chosen to disεolve in, or covalently bind to εuεpendible particleε, provided, however, that the photosensitizer and the photoactive indicator precursor are not associated with the same particle. When noncovalently bound, the compounds and the particles will all usually be hydrophobic to reduce the ability of the compoundε to diεεociate from the particles and to associate with the same particle. The problem of having both the photosensitizer and the photoactive indicator associated with the same particle may be minimized by covalently binding either one or both of the compounds to a particle, thereby allowing each compound to be either hydrophilic or hydrophobic. The number of photosensitizer or photoactive indicator precursor molecules aεsociated with each particle will be at least one and may be sufficiently high enough so that the particle consists entirely of photosensitizer or photoactive indicator precursor molecules. The preferred number of molecules will be selected empirically to provide the highest signal to background in the asεay (where the signal is determined under conditions where the particles are bound to each other and the background is determined where the particles are unasεociated) . Normally, the concentration of photoεenεitizer and photoactive indicator precurεor in the particleε will range from 10"* to 5M, usually from 10 "5 to 10 _1 M, preferably from 10 "3 to lO ' tø. "Oil droplets" refers to fluid or waxy particles comprised of a lipophilic compound coated and stabilized with an emulsifier that iε an amphiphilic molecule εuch aε, for example, phoεpholipids, sphingomyelin, albumin and the like. The phospholipids are baεed upon aliphatic carboxylic acid esters of aliphatic polyols, where at least one hydroxylic group iε εubεtituted with a carboxylic acid ester of from about 8 to 36, more usually of from about 10 to 20 carbon atoms, which may have from 0 to 3 sites, more usually from 0 to 1 site of ethylenic unsaturation and at least 1, normally only 1, hydroxyl group substituted with phosphate to form a phosphate ester. The phosphate group may be further substituted with small aliphatic compounds which are of di or higher functionality, generally having hydroxyl or amino groups. The oil droplets can be made in accordance with conventional procedures by combining the appropriate lipophilic compounds with a surfactant, anionic, cationic or nonionic, where the surfactant is present in from about 0.1 to 40, more usually from about 0.1 to 20 weight percent of the mixture and subjecting the mixture in an aqueouε medium to agitation, εuch aε εonication or vortexing. Illuεtrative lipophilic compoundε include hydrocarbon oilε, halocarbonε including fluorocarbons, alkyl phthalateε, trialkyl phosphates, triglycerides, etc. An εbp member will uεually be adεorbed to the εurface of the oil droplet or bonded directly or indirectly to a εurface component of the oil droplet. The sbp member may be incorporated into the liquid particleε either during or after the preparation of the liquid particleε. The sbp member will normally be present in from about 0.5 to 100, more uεually 1 to 90, frequently from about 5 to 80 and preferably from about 50 to 100 mole percent of the moleculeε present on the εurface of the particle. The following is a list, by way of illustration and not limitation, of amphiphilic compoundε, which may be utilized for εtabilizing oil dropletε: phoεphatidyl ethanolamine, phoεphatidyl choline, phoεphatidyl serine, di yristoylphoεphatidyl choline, egg phoεphatidyl choline, diapalmitoylphosphatidyl choline, phoεphatidic acid, cardiolipin, lecithin, galactocerebroεide, εphingomyelin, dicetylphoεphate, phoεphatidyl inoεitol, 2-trihexadecylammoni__methylamine, 1,3-bis(octadecyl phosphate) -propanol, εtearoyloxyethylene phoεphate, phoεpholipidε, dialkylphoεphateε, εodiu dodecyl εulfate, cationic detergentε, anionic detergentε, proteinε such as albumin, non-ionic detergents, etc. Stabilization of oil dropletε can alεo be achieved by coating with a polymer εuch aε polycyanoacrylates, dextran, polymerized proteins such aε albumin, hydroxybutyl methacrylate, polyacrylamide and the like. Other compoundε may also be used which have lipophilic groupε and which have been described previously. For the most part, theεe compounds will be alkylbenzenes, having alkyl groups of from 6 to 20 carbon atoms, usually mixtures of alkyl groupε, which may be straight or branched chain, and having a carboxyl group, an hydroxylic group, a polyoxy alkylene group (alkylene of from 2 to 3 carbon atomε) , carboxylic group, sulfonic acid group, or amino group. Aliphatic fatty acids may be used which will normally be of from about 10 to 36, more usually of from about 12 to 20 carbon atomε. Alεo, fatty alcoholε having the carbon limitε indicated for the fatty acidε, fatty amineε of similar carbon limitations and various εteroidε may also find use. The oil dropletε can compriεe a fluorocarbon oil or a εilicone oil (εilicon particle) . Such dropletε are deεcribed by Giaever in U.S. Patents Nos. 4,634,681 and 4,619,904 (the diεcloεureε of which are incorporated herein in their entirety) . These droplets are formed by dispersing a fluorocarbon oil or silicone oil in an aqueouε phase. The droplets are prepared by placing a small amount of the selected oil (generally, such oils are commercially available) in a container with a larger amount of the aqueous phase. The liquid εyεtem iε εubjected to agitation to bring about emulεification and then centrifuged. The homogeneous phase is removed and the residual droplets are resuεpended in an aqueous buffered medium. The above centrifugation and decantation εtepε can be repeated one or more times before the droplets are utilized. Sbp members can be bound to the droplets in a number of ways. As described by Giaever, the particular sbp member, particularly a proteinaceouε sbp member, can be coated on the dropletε by introducing an excess of the εbp member into the aqueouε medium prior to or after the emulsification step. Washing steps are desirable to remove excess sbp member. Functionalization of the oil introduces functionalities deεcribed above for linking to εbp members. Such functionalities can also be employed to link the dropletε to a photoεenεitizer or a photoactive indicator precursor. On the other hand, the photosenεitizer or photoactive indicator precursor will frequently be chosen to be soluble in the oil phase of the oil droplet and will not be covalently bound. When the oil is a fluorocarbon, a fluorinated photosenεitizer or photoactive indicator precursor will often be more soluble than the corresponding unfluorinated derivation. "Liposomes" refers to microvesicles of approximately εpherical εhape and are one of the preferred materialε for uεe in the preεent invention. The lipoεomes have a diameter that iε at leaεt about 20 nm and not more than about 20 micronε, usually at least about 40 nm and lesε than about 10 micronε. Preferably, the diameter of the lipoεomeε will be leεε than about two micronε so aε to limit settling or floatation. The outer shell of a liposome consistε of an amphiphilic bilayer that encloεeε a volume of water or an aqueouε εolution. Lipoεomeε with more than one bilayer are referred to aε multilamellar vesicles. Liposomes with only one bilayer are called unilamellar vesicles. Multilamellar vesicleε are preferred in the present invention when using a lipophilic photosensitizer or photoactive indicator precursor becauεe of their ability to incorporate larger quantitieε of theεe materialε than unilamellar veεicleε. The amphiphilic bilayer iε frequently compriεed of phospholipids. Phospholipidε employed in preparing particles utilizable in the present invention can be any phospholipid or phospholipid mixture found in natural membranes including lecithin, or εynthetic glyceryl phoεphate diesters of saturated or unsaturated 12-carbon or 24-carbon linear fatty acidε wherein the phoεphate cεin be preεent aε a monoeεter, or as an ester of a polar alcohol such as ethanolamine, choline, inositol, serine, glycerol and the like. Particularly preferred phoεpholipids include L-α-palmitoyl oleoyl-phoεphatidylcholine (POPC) , palmitoyl oleoylphosphatidyl-glycerol (POPG) , -α-dioleoylphosphatidylglycerol, -α- (dioleoyl) -phoεphatidyl ethanolamine (DOPE) and L-α- (dioleoyl) - phosphatidyl β- (4- (lV-maleimidomethyl) -cyclohexane-1-carboxyamido)ethanol (DOPE-MCC) . The phospholipids in the bilayer may be εupplemented with choleεterol and may be replaced with other amphiphilic compoundε that have a polar head group, usually charged, and a hydrophobic portion usually compriεed of two linear hydrocarbon chainε. Exampleε of εuch εubstituentε include dialkylphoεphate, dialkoxypropylphoεphates wherein the alkyl groups have linear chainε of 12 to 20 carbon atomε, N- (2,3-di- (9- (Z) -octa-decenyloxy) ) - prop -l -yl -W,-T,_\t-trimethyl-ammonium chloride (DOTMA) , εphingomyelin, cardiolipin, and the like. Lipoεomes utilized in the present invention preferably have a high negative charge density to stabilize the suspension and to prevent εpontaneouε aggregation. Liposomes may be produced by a variety of methods including hydration and mechanical disperεion of dried phoεpholipid or phoεpholipid εubεtitute in an aqueouε εolution. Liposomes prepared in this manner have a variety of dimenεionε, compoεitions and behaviors. One method of reducing the heterogeneity and inconεiεtency of behavior of mechanically diεpersed liposomes iε by sonication. Such a method decreaseε the average liposome size. Alternatively, extrusion iε uεable aε a final step during the production of the lipoεomeε. U.S. Patent 4,529,561 discloseε a method of extruding liposomes under pressure through a uniform pore-size membrane to improve size uniformity. For use in the present invention the liposomeε should be capable of binding to an εbp member and be capable of having a photoεenεitizer or photoactive indicator precurεor aεεociated with either the aqueouε or the nonaqueouε phaεe. The lipoεomeε utilized in the present invention will usually have sbp members bound to the outer surface of the lipid vesicle. Preparation of liposomes containing a hydrophobic or amphiphilic photosensitizer or a photoactive indicator precursor diεεolved in the lipid bilayer can be carried out in a variety of methods, including a method described by Olsen, et al., Biochemica et Biophysica Acta, 557(9) . 1979. Briefly, a mixture of lipidε containing the appropriate compound in an organic εolvent εuch aε chloroform is dried to a thin film on the walls of a glasε vessel. The lipid film is hydrated in an appropriate buffer by shaking or vortexing. Thereafter, the lipid suspension iε extruded through a series of polycarbonate filter membranes having succeεεively εmaller pore εizeε, for example, 2.0, 1.0, 0.8, 0.6, 0.4, and 0.2 microns. Repeated filtration through any of the filters, and in particular through the εmalleεt filter, iε deεirable. The liposomes can be purified by, for example, gel filtration, such as through a column of Sephacryl S-1000. The column can be eluted with buffer and the lipoεomeε collected. Storage in the cold prolongs shelf-life of the liposomes produced by this method. Alternatively the photoεenεitizer or photoactive indicator precurεor can be added to the liquid suspenεion following preparation of the liposomes. Labeling of droplets and liposomes will often involve, for example, inclusion of thiol or maleimide or biotin groups on the molecules comprising the lipid bilayer. Photosenεitizerε, photoactive indicator precurεor moleculeε or εbp members may then be bound to the surface by reaction of the particles with one of these materialε that iε bound to a εulfhydryl reactive reagent, a εulfhydryl group, or avidin, reεpectively. Sulfhydryl reactive groups include alkylating reagents such as bromoacetamide and maleimide. Sbp members can be attracted to the εurface of the lipoεome particles by weak hydrophobic interactions, however εuch interactionε are not generally εufficient to withεtand the shear force encountered during incubation and washing. It is preferable to covalently bond sbp memberε to a lipoεome particle that has been functionalized, for example by use of DOPE-MCC, as shown above, by combining said liposome with the εelected εbp member functionalized with a mercaptan group. For example, if the sbp member is an antibody, it may be reacted with S-acetyl-mercaptosuccinic anhydride ' (SAMSA) and hydrolyzed to provide a sulfhydryl modified antibody. "Latex particles" refers to a particulate water-εuεpendible water-insoluble polymeric material usually having particle dimensions of 20 nm to 20 mm, more preferably 100 to 1000 nm in diameter. The latex is frequently a subεtituted polyethylene εuch aε the following: polyεtyrene-butadiene, polyacrylamide polyεtyrene, polyεtyrene with amino groupε, poly-acrylic acid, polymethacrylic acid, acrylonitrile-butadiene, εtyrene copolymerε, polyvinyl acetate-acrylate, polyvinyl pyridine, vinyl-chloride acrylate copolymers, and the like. Non-crosεlinked polymerε of εtyrene and carboxylated styrene or styrene functionalized with other active groupε such as amino, hydroxyl, halo and the like are preferred. Frequently, copolymerε of εubstituted styreneε with dieneε εuch aε butadiene will be uεed. The aεεociation of the photosensitizer or photoactive indicator precursor with latex particles utilized in the present invention may involve incorporation during formation of the particles by polymerization but will uεually involve incorporation into preformed particleε, uεually by noncovalent diεεolution into the particles. Usually a solution of the photoactive indicator precurεor or photoεenεitizer will be employed. Solventε that may be utilized include alcoholε (including ethanol) , ethylene glycol and benzyl alcohol; amideε εuch aε dimethyl formamide, formamide, acetamide and tetramethyl urea and the like; εulfoxides such as dimethyl sulfoxide and sulfolane; and ethers such as carbitol, ethyl carbitol, dimethoxy ethane and the like, and water. The use of solvents having high boiling points in which the particleε are inεoluble permits the use of elevated temperatureε to facilitate diεεolution of the compounds into the particles and are particularly suitable. The solventε may be uεed singly or in combination. Particularly preferred solvents for incorporating a photoεenεitizer are those that will not quench the triplet excited state of the photosensitizer either because of their intrinεic properties or because they can subsequently be removed from the particles by virtue of their ability to be disεolved in a εolvent such as water that is insoluble in the particles. Aromatic solventε are preferred, and generally εolvents that are soluble in the particle. For incorporating photoactive indicator precursorε in particles a solvent should be selected that doeε not interfere with the fluoreεcence of the photoactive indicator so formed because of their intrinsic properties or ability to be removed from the particleε. Frequently, aromatic εolventε will alεo be preferred. Typical aromatic εolventε include dibutylphthalate, benzonitrile, naphthonitrile, dioctylterephthalate, dichlorobenzene, diphenylether, dimethoxybenzene, etc. Except when the photoεensitizer or photoactive indicator precursor is to be covalently bound to the particles, it will usually be preferable to use electronically neutral photosenεitizers or photoactive indicator precursorε. It iε preferable that the liquid medium selected does not soften the polymer beads to the point of εtickineεε. A preferred technique comprises εuεpending the selected latex particleε in a liquid medium in which the photoεensitizer or photoactive indicator precursor has at least limited εolubility. Preferably, the concentrationε of the photosensitizer and photoactive indicator precursor in the liquid media will be selected to provide particles that have the highest efficiency of εinglet oxygen formation and higheεt quantum yield of emission from the photoactive indicator so formed in the media but less concentrated solutions will sometimes be preferred. Distortion or dissolution of the particles in the εolvent can be prevented by adding a miscible cosolvent in which the particleε are inεoluble. Generally, the temperature employed during the procedure will be choεen to maximize the εinglet oxygen formation ability of the photosensitizer-labeled particles and the quantum yield of the photoactive indicator so formed from the photoactive indicator precursor-labelled particleε with the proviεo that the particleε εhould not become aggregated at the selected temperature. Elevated temperatures are normally employed. The temperatureε for the procedure will generally range from 20°C to 200°C, more usually from 50°C to 170°C. It has been observed that εome compoundε that are nearly inεoluble in water at room temperature, are εoluble in, for example, low molecular weight alcoholε, such as ethanol and ethylene glycol and the like, at elevated temperatureε. Carboxylated modified latex particleε have been shown to tolerate low molecular weight alcohols at such temperatures. An sbp member may be phyεically adεorbed on the surface of the latex particle or may be covalently bonded to the particle. In caseε wherein the εbp member iε only weakly bound to the εurface of the latex particle, the binding may in certain caεeε be unable to endure particle-to-particle εhear forceε encountered during incubation and waεhings. Therefore, it is usually preferable to covalently bond εbp memberε to the latex particles under conditions that will minimize adsorption. This may be accompliεhed by chemically activating the εurface of the latex. For example, the _\t-hydroxyεuccinimide eεter of surface carboxyl groups can be formed and are then contacted with a linker having amino groups that will react with the ester groups or directly with an sbp member that has an amino group. The linker will usually be selected to reduce nonspecific binding of asεay components to the particle surface and will preferably provide suitable functionality for both attachment to the latex particle and attachment of the εbp member. Suitable materialε include maleimidated aminodextran (MAD), polylyεine, aminoεaccharideε, and the like. MAD can be prepared as described by Hubert, et al . , Proc. Natl . Acad. Sci . , 25.(7), 3143, 1978. In one method, MAD iε firεt attached to carboxyl-containing latex particleε using a water soluble carbodiimide, for example, 1- (3-dimethylaminopropyl) -3-ethyl carbodiimide. The coated particles are then equilibrated in reagents to prevent nonspecific binding. Such reagents include proteins εuch aε bovine gamma globulin (BGG) , and detergent, such as Tween 20, TRITON X-100 and the like. An sbp member having a εulfhydryl group, or εuitably modified to introduce a εulfhydryl group, iε then added to a εuspension of the particleε, whereupon a covalent bond iε formed between the εbp member and the MAD on the particleε. Any exceεε unreacted εbp member can then be removed by waεhing. "Metal sols" refers to those suspendible particles comprised of a heavy metal, i.e., a metal of atomic number greater than 20 εuch aε a Group IB metal, e.g. , gold or εilver. Metal εol particleε are deεcribed, for example, by Leuvering in U.S. Patent No. 4,313,734, the disclosure of which is incorporated herein by reference in its entirety. Such sols include colloidal aqueous disperεion of a metal, metal compound, or polymer nuclei coated with a metal or metal compound. The metal sols may be of metals or metal compoundε, εuch aε metal oxides, metal hydroxides and metal εalts of polymer nuclei coated with metals or metal compoundε. Exampleε of such metals are platinum, gold, εilver, mercury, lead, palladium, and copper, and of εuch metal compoundε are εilver iodide, εilver bromide, copper hydrous oxide, iron oxide, iron hydroxide or hydrous oxide, aluminum hydroxide or hydrous oxide, chromium hydroxide or hydrous oxide, vanadium oxide, arsenic sulphide, manganese hydroxide, lead sulphide, mercury sulphide, barium sulphate and titanium dioxide. In general, the metalε or metal compoundε useful may be readily demonεtrated by meanε of known techniqueε. It iε sometimes advantageous to use solε compriεed of diεpersed particleε conεiεting of polymer nuclei coated with the above mentioned metalε or metal compounds. These particles have similar properties as the dispersed phase of pure metalε or metal compoundε, but εize, denεity and metal contact can be optimally combined. The metal εol particleε may be prepared in a large number of wayε which are in themselves known. For example, for the preparation of a gold sol Leuvering refers to an article by G. Frenε in .Nature Physical Science 241, 20 (1973) . The metal sol particles can be modified to contain various functional groupε as deεcribed above for linking to an sbp member or a photosensitizer or a photoactive indicator precursor. For example, polymeric bonding agents can be uεed to coat the particleε such as polymerε containing thiol groupε that bond εtrongly to many heavy metalε or εilylating agentε that can bond and form polymeric coatingε as, for example, by reaction of metal particles with trialkoxy aminoalkylεilaneε as described in European Published Patent Application 84400952.2 by Advanced Magneticε for coating magnetic particles. "Dye crystallites" refers to microcryεtals of pure or mixed solid water inεoluble dyes, preferably dyeε that can εerve aε the photoεensitizers deεcribed above. The dye cryεtalliteε uεeful in the preεent invention have a size range of 20 nm to 20 μm. One method for preparing dye crystallites is deεcribed in U.S. Patent No. 4,373,932 (Gribnau, et al.), the disclosure of which is incorporated herein by reference in its entirety. Gribnau describeε colloidal dye particleε and aqueous disperεions of a hydrophobic dye or pigment, which may have an immunochemically reactive component directly or indirectly attached. The dye particles are prepared in general by disperεing a dye in water and then centrifuging. A dye pellet iε obtained and reεuspended in water, to which glass beads are added. This suεpenεion iε rolled for εeveral days at room temperature. The liquid is decanted and centrifuged, and the dye particleε are obtained after aspiration of the liquid. Another method for preparing dye crystallites is by slow addition of a solution of the dye in a water miscible εolvent to water. Another method iε by εonication of a εuεpenεion of the εolid dye in water. Binding of εbp members to the dye particleε can be achieved by direct or indirect adεorption or covalent chemical attachment. The latter is governed by the presence of εuitable functional groupε in any coating material and in the dye. For example, functional groups can be introduced onto the surface of a dye crystallite by coupling a compound containing a diazotized aromatic amino group and the desired functional group to a phenolic or anilino group of the dye. Where the dye has a carboxyl group, the dye crystallite can be activated by a carbodiimide and coupled to a primary amino component. Aliphatic primary amino groups and hydroxyl groupε can be activated, for example, by cyanogen bromide or halogen-substituted di- or tri-azines, after which attachment with a primary amino component or, for example, with a component containing a -SH or -OH group can take place. Use can alεo be made of bifunctional reactive compoundε. For example, glutaraldehyde can be uεed for the mutual coupling of primary amino componentε of the dye and an εbp member, and, for example, a hetero-bifunctional reagent such as -V-succinimidyl 3- (2-pyridyldithio) propionate can be employed for the coupling of a primary amino component to a component containing a thiol group. "Wholly or partially sequentially" refers to the condition when the components of the methods of the present invention are combined other than concomitantly (simultaneouεly) , one or more may be combined with one or more of the remaining agents to form a subcombination. Each subcombination can then be subjected to one or more steps of the present method. Thus, each of the εubcombinationε can be incubated under conditionε to achieve one or more of the deεired reεults. Various ancillary materialε will frequently be employed in the aεεay in accordance with the present invention. For example, buffers will normally be present in the aεεay medium, aε well aε stabilizers for the asεay medium and the aεεay componentε. Frequently, in addition to theεe additives, proteinε may be included, such as albumins, organic solventε εuch as formamide, quaternary ammonium saltε, polycationε such as dextran sulfate, surfactants, particularly non-ionic εurfactantε, binding enhancerε, e.g. , polyalkylene glycolε, or the like. Description of the Specific Embodiments In general, the preεent invention iε directed to methodε for determining an analyte in a selected medium. The methodε compriεe treating a medium suspected of containing an analyte under conditions such that the analyte, if present, affects the amount of a photosensitizer and a photoactive indicator precursor that can come into close proximity wherein the short-lived εinglet oxygen generated by the photosensitizer can react with the photoactive indicator precurεor prior to the spontaneous decay of the singlet oxygen in order to form a photoactive indicator. The method further comprises exposing the photoactive indicator to light which may be of the εame or a different wavelength than the light uεed to excite the photoεensitizer in order to excite the photoactive indicator so formed and then measuring the intensity of fluorescence emitted from the photoactive indicator upon excitation. The intenεity of fluorescence produced iε related to the amount of analyte in the medium. The photoactive indicator iε formed upon reaction of the photoactive indicator precurεor with the εinglet oxygen generated by the photoεenεitizer. The photosensitizer catalyzes the generation of singlet oxygen usually in responεe to photoexcitation followed by energy tranεfer to molecular oxygen. Often one or both of the photoεenεitizer and the photoactive indicator precursor will be associated with surfaces, wherein, in homogeneous assays, the surface will preferably be the surface of suspendible particles. For homogeneouε assays the invention is predicated on an analyte causing or inhibiting molecules of the photosensitizer and the photoactive indicator precurεor to be closer to each other than their average distance in the bulk solution of the aεεay medium. The amount of this partitioning will depend upon the amount of analyte present in the sample to be analyzed. The photosenεitizer moleculeε that do not become aεsociated with the photoactive indicator precurεor produce singlet oxygen that is unable to reach the photoactive indicator precurεor before undergoing decay in the aqueouε medium. However, when the photosensitizer and the photoactive indicator precursor come in close proximity with each other in response to the presence of the analyte, the εinglet oxygen produced upon irradiation of the photosensitizer can react with the photoactive indicator precursor to form a photoactive indicator before undergoing decay. Because numerous photoactive indicator precursor moleculeε and/or photosensitizer molecules can be associated with a surface or can be incorporated into the material comprising the surface, the presence of a εurface in conjunction with the photoεensitizer and photoactive indicator precurεor can increaεe the efficiency of, or action of, εinglet oxygen with the photoactive indicator precurεor prior to decay. It iε therefore preferred to bring one member of the photoactive indicator precurεor and photosenεitizer pair into the proximity of a surface that incorporates the other member aε a function of the preεence of an analyte. The subject asεay provideε for a convenient method for detecting and meaεuring a wide variety of analyteε in a εimple, efficient, reproducible manner, which can employ εimple equipment for meaεuring the amount of light produced during the reaction. The amount of photoεensitizer that comes in close proximity to the photoactive indicator precurεor is affected by the presence of analyte by virtue of the photosenεitizer and photoactive indicator precurεor each being aεεociated with an εbp member. Thiε may be accompliεhed in a number of ways and the term "asεociated with" iε defined thereby. The photosenεitizer and photoactive indicator precurεor may contain functionalitieε for covalent attachment to εbp memberε and the εbp members may contain functionalities for attaching to the photoεenεitizer and/or photoactive indicator precurεor. The attachment may be accompliεhed by a direct bond between the two moleculeε or through a linking group which can be employed between an εbp member and the photoεensitizer or photoactive indicator precurεor. In another embodiment either or both of the photosenεitizer and photoactive indicator precurεor can be bound to εurfaceε or incorporated in particles, to which are also attached sbp memberε. In both caseε each of the εbp memberε iε capable of binding directly or indirectly to the analyte or an aεεay component whose concentration is affected by the preεence of the analyte. Either or both of the photosenεitizer and photoactive indicator precurεor can be incorporated into particles by virtue of being dissolved in at least one phase of the particles, in which case the solute will be at much higher concentration within the particle than in the bulk aεεay medium. Alternatively, either or both of the photoεenεitizer and photoactive indicator precurεor may be covalently bound to particleε, either by providing linking functional groups on the components to be bound or by incorporating the photoεensitizer or photoactive indicator precursor into a polymer that compriεeε the particles. For particles that are oil droplets or liposomeε the photosenεitizer and photoactive indicator precurεor can be attached to one or more long hydrocarbon chainε, each generally having at leaεt 10 to 30 carbon atoms. If the particleε are dropletε of a fluorocarbon, the photosensitizer or photoactive indicator precursor incorporated into these particles may be fluorinated to enhance solubility and reduce exchange into other particles bound with the other label, and the hydrocarbon chain used for linking will preferably be replaced with a fluorocarbon chain. For silicon fluid particles the photosensitizer and photoactive indicator precursor can be bound to a polyεiloxane. In order to maximize the number of photoεensitizer or photoactive indicator precursor molecules per particle, it will usually be deεirable to minimize the charge and polarity of the photoεenεitizer or photoactive indicator precurεor so that it reεideε within the non-aqueouε portion of the particle. When the particle is a liposome and it is desired to retain the photosensitizer or photoactive indicator precursor in the aqueous phaεe of the lipoεome, it will be preferred to uεe photosensitizers or photoactive indicator precurεors that are highly polar or charged. No matter how the photosensitizer and the photoactive indicator precursor are associated with their respective εbp member, it is critical that neither compound is capable of dissociating from its sbp member and becoming associated with the sbp member associated with the other member of the photosenεitizer and photoactive indicator precursor pair during the course of the assay. Thus, dissociation of these compoundε from their respective sbp members must be slow relative to the time required for the assay. The photoactive indicator precursor may be bound to an sbp member that is capable of binding directly or indirectly to the analyte or to an assay component whose concentration is affected by the presence of the analyte. The term "capable of binding directly or indirectly" means that the designated entity can bind specifically to the entity (directly) or can bind specifically to a specific binding pair member or to a complex of two or more sbp members which is capable of binding the other entity (indirectly) . The εurface generally has an sbp member bound to it. Preferably, the photoactive indicator precursor is asεociated with the εurface, uεually within a εuεpendible particle. Thiε sbp member iε generally capable of binding directly or indirectly to the analyte or a receptor for the analyte. When the sbp members associated with the photosensitizer and the photoactive indicator precurεor are both capable of binding to the analyte, a εandwich aεεay protocol can be used. When one of the εbp memberε 5 aεεociated with the photoεensitizer or photoactive indicator precursor can bind both the analyte and an analyte analog, a competitive asεay protocol can be used. The attachment to a surface or incorporation in a particle of the photoactive indicator precursor is governed generally by the same principles described above for the attachment to, or the incorporation 10 into, a particle of the photoεensitizer. The photosenεitizer iε usually caused to activate the photoactive indicator precurεor by irradiating the medium containing theεe reactantε. Since it will frequently be undesirable to excite the photoactive indicator precursor directly with light, the wavelength of light used to activate the 15 photosensitizer will uεually be longer than the longeεt wavelengthε abεorbed εubεtantially by the photoactive indicator precursor. However, the medium must be irradiated with a εhort enough wavelength of light that haε εufficient energy to convert the photoεensitizer to an excited state and thereby render it capable of activating molecular oxygen to singlet 20 oxygen. The excited state for the photosensitizer capable of exciting molecular oxygen is generally a triplet state which is more than about 20, usually at leaεt 23 Kcal/mol more energetic than the photosenεitizer ground εtate. Preferably, the medium iε irradiated with light having a wavelength of about 450 to 950 nm although shorter wavelengths can be used, for 25 example, 230 to 950 nm, and longer wavelengths of up to 2000 nm can be used by providing sufficiently intense light to provide for biphotonic excitation. Although it will usually be preferable to excite the photosenεitizer by irradiation with light of a wavelength that iε efficiently abεorbed by 30 the photoεensitizer, other meanε of excitation may be used, for example, by energy transfer from an excited state of an energy donor. When an energy donor iε used, wavelengths of light can be uεed which are inefficiently abεorbed by the photoεensitizer but are efficiently abεorbed by the energy donor. The energy donor may be bound to an aεsay component that is 35. associated, or becomes associated, with the photoεensitizer, for example, bound to a surface or incorporated in the particle having the photosenεitizer. When an energy donor is employed its loweεt energy εinglet and/or triplet εtate will usually be of higher energy than the lowest energy εinglet and/or triplet εtate, respectively, of the 40 photosenεitizer. The εinglet oxygen so formed reacts with the photoactive indicator precursor to form a photoactive indicator which is fluorescent. Fluorescence of the photoactive indicator that iε formed can be detected following electronic excitation of the photoactive indicator. Normally 45 electromagnetic radiation, preferably light, will be uεed to excite the photoactive indicator, but energy tranεfer from molecules that have been excited by other means such as chemiexcitation can also be used when the chemiexcitation is εeparate from the above-mentioned εinglet oxygen reaction. The wavelength of light used to excite the photoactive indicator can be the same or different from the wavelength of light uεed to excite the photoεenεitizer. Uεually it will be preferable for the light emitted by the photoactive indicator to be εhorter wavelength than any fluoreεcence of the photoεensitizer. Preferably, therefore, when the photoεenεitizer iε fluoreεcent, the light uεed to excite the photoactive indicator will be shorter wavelength than that used to activate the photosensitizer, usually at leaεt 50 nm shorter, preferably at least 200 nm shorter. The fluorescence emitted from the excited photoactive indicator may be measured in any convenient manner such as photographically, visually or photometrically, to determine the amount thereof, which is related to the amount of analyte in the medium. Irradiation of the photosensitizer and the excitation of the photoactive indicator may be carried out simultaneouεly but will preferably be carried out εequentially εo that the light uεed to excite the photoεensitizer does not interfere with the fluorescence measurement. The photoactive indicator precursor must not substantially absorb light at the wavelength used to generate the singlet oxygen and will therefore usually absorb at shorter wavelengths than the photosensitizer. In addition, the photoactive indicator precursor will preferably not abεorb εignificantly at the wavelength required to excite the photoactive indicator and therefore will uεually absorb at shorter wavelengths than the photoactive indicator. The method and compoεitionε of the invention may be adapted to most asεays involving εbp members such as ligand-receptor; e.g. , antigen-antibody reactions; polynucleotide binding asεays, and so forth. The asεayε may be homogeneous or heterogeneous, competitive or noncompetitive. The assay components, photoactive indicator precursor and photosensitizer, can be asεociated in a number of ways to a receptor, to a ligand, or, when employed, to a surface. The asεociation may involve covalent or non-covalent bondε. Thoεe εkilled in the art will be able to chooεe appropriate associations depending on the particular asεay deεired in view of the foregoing and the following illuεtrative diεcuεsion. The εample may be pretreated if neceεεary to remove unwanted materialε. The reaction for a noncompetitive sandwich type asεay can involve an εbp member, (e.g. , an antibody, polynucleotide probe, receptor or ligand) complementary to the analyte and associated with a photoactive indicator precurεor; a photoεenεitizer associated with an sbp member, (e.g. , antibody, polynucleotide probe, receptor or ligand) that is also complementary to the analyte; the εample of intereεt; and any ancillary reagentε required. In a competitive protocol one εbp member can be a derivative of the analyte and the other εbp member can be complementary to the analyte, e.g. , an antibody. In either protocol the componentε may be combined either εimultaneouεly or wholly or partially εequentially. The ability of εinglet oxygen produced by an activated photoεenεitizer to react with the photoactive indicator precursor to form a photoactive indicator is governed by the binding of an sbp member to the analyte. Hence, the presence or amount of analyte can be determined by measuring the amount of light emitted upon activation of the photoactive indicator so formed by irradiation. Both the binding reaction and detection of the extent thereof can be carried out in a homogeneouε εolution without separation, wherein, preferably, one or both of the photosensitizer and the photoactive indicator precursor are incorporated in particleε to which the εbp memberε are attached. Thiε iε an advantage of the present invention over prior art methods utilizing chemiluminescence. In a heterogeneous asεay approach, one of the εbp memberε will frequently be bound to a εupport or another means provided to separate it from the aεεay medium. The εupport may be either a non-diεpersible εurface or a particle. In one embodiment, the support or particle will have associated with it one member of a group conεiεting of the photoactive indicator precursor and the photosensitizer. Another εbp member will have the other member of the group associated with it wherein the sbp memberε can independently, either directly or indirectly, bind the analyte or a receptor for the analyte. These components are generally combined either εimultaneouεly or wholly or partially εequentially. The εurface or particleε are then separated from the liquid phase and either are subjected to conditions for activating the photosenεitizer and the photoactive indicator εo formed, uεually by irradiating the separated phase, and measuring the amount of fluorescence emitted. Alternatively, a heterogenous asεay of thiε invention may be carried out by providing meanε εuch as a εurface to εeparate a first sbp member from the liquid assay medium and providing a second sbp member that iε aεεociated with a photoεenεitizer and that bindε to the first sbp member as a function of the amount of analyte in the medium. The sample εuspected of containing the analyte iε then combined with the firεt and second sbp memberε either εimultaneously or wholly or partially sequentially and the firεt sbp member is εeparated from the medium. A third sbp member associated with a photoactive indicator precursor iε then combined with the εeparated firεt εbp member where the third εbp member is capable of binding directly or indirectly to the second sbp member. The combination is then irradiated to activate the photoεensitizer and the fluorescence of the photoactive indicator so formed iε measured. The binding reactions in an asεay for the analyte will normally be carried out in an aqueouε medium at a moderate pH, generally that which provides optimum asεay sensitivity. Preferably, the activation of the photosensitizer will also be carried out in an aqueouε medium. However, when a εeparation εtep iε employed, non-aqueouε media such as, e.g. , acetonitrile, acetone, toluene, benzonitrile, etc. and aqueous media with pH values that are very high, i.e., greater than 10.0, or very low, i.e., less than 4.0, preferably with pH values that are very high, can be used. Aε explained above, the aεεay can be performed either without εeparation (homogeneouε) or with εeparation (heterogeneouε) of any of the aεεay componentε or products. The aqueous medium may be solely water or may include from 0.01 to 80 volume percent of a cosolvent but will usually include lesε than 40% of a cosolvent when an sbp member is used that is a protein. The pH for the medium of the binding reaction will usually be in the range of about 4 to 11, more usually in the range of about 5 to 10, and preferably in the range of about 6.5 to 9.5. The pH will usually be a compromise between optimum binding of the binding members and the pH optimum for the production of signal and the stability of other reagents of the asεay. Uεually no change in pH will be required for signal production, although if desired, a step involving the addition of an acid or a basic reagent can be inserted between the binding reaction and generation of εinglet oxygen and/or signal production. Usually in homogenous assayε the final pH will be in the range of 5 to 13. For heterogenouε assays non-aqueous solventε may also be used as mentioned above, the main consideration being that the εolvent not react efficiently with singlet oxygen. Various buffers may be uεed to achieve the deεired pH and maintain the pH during an aεsay. Illustrative buffers include borate, phosphate, carbonate, tris, barbital and the like. The particular buffer employed iε not critical to thiε invention, but in an individual assay one or another buffer may be preferred. Moderate temperatureε are normally employed for carrying out the binding reactionε of proteinaceouε ligandε and receptors in the asεay and uεually conεtant temperature, preferably, 25° to 40°, during the period of the meaεurement. Incubation temperatures for the binding reaction will normally range from about 5° to 45°C, usually from about 15° to 40°C, more uεually 25° to 40°C. Where binding of nucleic acidε occur in the assay, higher temperatures will frequently be used, usually 20° to 90°, more usually 35° to 75°C. Temperatureε during meaεurementε, that iε, generation of εinglet oxygen and light detection, will generally range from about 20° to 100°, more usually from about 25° to 50°C, more usually 25° to 40°C. The concentration of analyte which may be asεayed will generally vary from about 10" 4 to below 10 "16 M, more usually from about 10"* to 10' 14 M. Considerations, εuch aε whether the assay is qualitative, semiquantitative or quantitative, the particular detection technique the concentration of the analyte of interest, and the maximum desired incubation times will normally determine the concentrationε of the variouε reagent . In competitive aεεayε, while the concentrationε of the variouε reagents in the asεay medium will generally be determined by the concentration range of intereεt of the analyte, the final concentration of each of the reagentε will normally be determined empirically to optimize the εenεitivity of the aεεay over the range. That iε, a variation in concentration of the analyte which is of significance εhould provide an accurately measurable signal difference. The concentration of the sbp members will depend on the analyte concentration, the deεired rate of binding, and the degree that the εbp members bind nonspecifically. Usually, the sbp members will be present in at leaεt the loweεt expected analyte concentration, preferably at least the highest analyte concentration expected, and for noncompetitive asεayε the concentrationε may be 10 to 10* timeε the higheεt analyte concentration but usually lesε than 10"* M, preferably leεs than 10 "6 M, frequently between 10 " " and 10" 7 M. The amount of photosenεitizer or photoactive indicator precurεor aεsociated with a sbp member will uεually be at least one molecule per sbp member and may be as high as 10 s , usually at leaεt 10 to 10 4 when the photoεenεitizer or photoactive indicator precurεor molecule iε incorporated in a particle. While the order of addition may be varied widely, there will be certain preferenceε depending on the nature of the aεεay. The εimpleεt order of addition iε to add all the materialε εimultaneouεly. Alternatively, the reagentε can be combined wholly or partially sequentially. When the asεay iε competitive, it will often be deεirable to add the analyte analog after combining the sample and an εbp member capable of binding the analyte. Optionally, an incubation εtep may be involved after the reagentε are combined, generally ranging from about 30 εecondε to 6 hours, more usually from about 2 minutes to 1 hour before the photoεensitizer is caused to generate singlet oxygen and the photoactive indicator is cauεed to fluoresce. In a particularly preferred order of addition, a first set of sbp members that are complementary to and/or homologous with the analyte are combined with the einalyte followed by the addition of εpecific binding pair memberε complementary to the firεt specific binding pair memberε, each associated with a different member of the group conεisting of a photosenεitizer and a photoactive indicator precurεor. The aεεay mixture, or a separated component thereof, iε irradiated firεt to produce εinglet oxygen and then later to produce meaεurable fluoreεcence. In a homogeneouε aεεay after all of the reagents have been combined, they can be incubated, if deεired. Then, the combination iε irradiated (at the neceεεary wavelengthε of light) and the reεulting fluoreεcence emitted is measured. The emitted fluorescence iε related to the amount of the analyte in the sample tested. The amounts of the reagentε of the invention employed in a homogeneouε asεay depend on the nature of the analyte. Generally, the homogeneouε asεay of the preεent invention exhibitε an increased senεitivity over known aεεayε εuch aε the EMIT ® aεεay. This advantage reεultε primarily because of the improved signal to noise ratio obtained in the preεent method. The following assays are provided by way of illustration and not limitation to enable one skilled in the art to appreciate the εcope of the preεent invention and to practice the invention without undue experimentation. It will be appreciated that the choice of analyteε, photoεenεitizers, photoactive indicator precursors, surfaces, particles and reaction conditions will be εuggeεted to thoεe skilled in the art in view of the discloεure herein in the exampleε that follow. In one embodiment of the invention a photoactive indicator precursor of the following formula (Im) : iε covalently linked to an antibody for human chorionic gonadotropin (HCG) to provide Reagent 1. The photoactive indicator precurεor, functionalized with a IvJ-hydroxyεuccinimidyl eεter of the carboxyl group, reactε with the amino groupε of the antibody. The linking group iε a carboxamide. The photosensitizer utilized is rose bengal, which is covalently bound to latex particleε having an average dimenεion of 0.5 micron. The latex particleε and rose bengal are covalently bound to each other by means of chloromethyl groups on the latex to provide an ester linking group as described in J. Am. Chem. Soc , 97.- 3741 (1975) . The latex particle iε further linked to a εecond antibody for HCG by means of .W-hydroxyεuccinimidyl eεter groupε on the latex to provide Reagent 2. Both of the antibodies employed are monoclonal antibodies prepared by standard hybrid cell line technology. One antibody recognizes the -.-εubunit of HCG and the other recognizes the β-subunit of HCG. In conducting the asεay a εerum sample suεpected of containing HCG iε obtained from a patient. Fifty microliterε of the εample is combined in 500 microliters of aqueous medium, buffered with Triε buffer at pH 8.0, with Reagent 1 and Reagent 2 above. The amountε of Reagent 1 and Reagent 2 are sufficient to provide concentrations of each antibody of about 10" 9 molar. The reaction mixture iε then incubated for a period of one hour at 25°C and then irradiated for 30 minuteε with 560 nm light. The fluorescence of the solution is then measured by irradiating at 350 nm and detecting at 440 nm and is compared with valueε obtained in a εimilar procedure with εampleε having known concentrationε of HCG to determine the concentration of HCG in the unknown. In an alternative approach baεed on the above, Reagent 2 iε roεe bengal covalently linked to the second antibody and no latex particle is employed. In still another alternative approach based on the above, Reagent 2 iε roεe bengal covalently linked to the εecond antibody and Reagent 1 iε the photoactive indicator precurεor covalently bound to latex particleε, to which the firεt antibody iε covalently attached. In εtill another alternative approach based on the above, Reagent 1 is as described immediately above, Reagent 2 is roεe bengal covalently linked to latex particleε, to which avidin iε covalently attached, and a third reagent (Reagent 2A) that is the second antibody covalently linked to biotin is employed. Reagent 1 and the third reagent are combined with sample and incubated. Then, an excesε of Reagent 2 iε added and the remaining procedure iε aε deεcribed above. In another embodiment in accordance with the present invention, a first set of oil droplets (Reagent 3) is prepared from a solution of the photosenεitizer and chlorophyll in mineral oil in accordance with Giaever, supra. The oil dropletε, which range from 0.1 to 2 micronε in diameter, are coated with a functionalized εurfactant that is linked to a monoclonal antibody for C-reactive protein (CRP) . The chlorophyll is lipophilic and is therefore dissolved in the lipophilic oil droplet. A second set of oil droplets (Reagent 4) iε prepared in a εimilar manner. In thiε εet of dropletε the oil droplet iε similarly coated with a second monoclonal antibody for CRP, which recognizes a different portion of the CRP molecule than that recognized by the first monoclonal antibody referred to above. 9-Benzal-10-methyl acridan iε irreversibly diεεolved in the lipophilic oil droplet by including a Jt,_\t-didodecylcarboxamide group bound to one of the phenyl groupε of the acridan. The monoclonal antibodieε are prepared by εtandard hybrid cell line technology. A serum sample εuεpected of containing CRP (50 microliterε) iε combined with exceεε quantities of Reagent 3 and Reagent 4 in an aqueous buffered medium (500 μL) at pH 7.5. The medium iε incubated at 25°C for a period of 20 minutes. The medium, without separation, iε irradiated at 633 nm uεing a He/Ne laεer for a period of twenty minuteε and the fluoreεcence of the solution is measured by irradiation at 360 nm and detection at 440 nm of the light emitted. The intensity of fluorescence is compared with that from εampleε containing known amountε of CRP and the amount of CRP in the unknown εample iε determined by comparing the valueε. In thiε way a convenient and εensitive homogeneous immunoassay for CRP iε conducted. In an alternative approach baεed on the above, Reagent 3 haε an antibody for fluoreεcein in place of the antibody for CRP and an additional reagent (Reagent 3A) haε the CRP antibody covalently linked to fluorescein. Reagent 4 has avidin in place of the second CRP antibody and a fourth reagent (Reagent 4A) has the εecond antibody covalently linked to biotin. In the assay Reagent 4A and Reagent 3A are combined with sample and incubated. Thereafter, Reagents 3 and 4 are added and incubated. The remainder of the assay procedure as described above is then carried out. In another embodiment of the present invention, one set of liposomes (Reagent 5) (0.2 micron in diameter) iε formed by high pressure extrusion of a phoεpholipid suspenεion in pH 7.4 buffer through a 0.2 micron pore membrane using a commercially available instrument deεigned for εuch purpose. A thyroxine analog is covalently linked to the liposome by firεt forming mercaptoacetamide groupε on the lipoεome by reaction of phoεphatidylethanolamine in the lipoεome with an _V-hydroxyεuccinimide eεter of methyl carboxymethyl diεulfide followed by reaction with dithioerythritol. Bromoacetyl thyroxine is then allowed to react with the sulfhydrylated liposomes. A metallo-porphyrin dye is dissolved in the lipophilic portion of the liposome. Another εet of lipoεomeε (Reagent 6) iε utilized to attach a monoclonal antibody for thyroxine. The antibody is attached covalently by means εimilar to the attachment of thyroxine. A photoactive indicator precurεor of the following formula: 0H iε covalently linked by meanε of a carboxamide linking group to the εurface of the lipoεome. Reagent 5 and Reagent 6 are combined in an aqueouε buffered aεsay medium (500 μL) of pH 8.0 together with a serum sample suspected of containing thyroxine that contains a thyroxine releasing agent of the following formula: to displace thyroxine from binding proteins (50 micro-liters) . The assay medium iε then incubated at room temperature for 1 hour. The medium iε irradiated at 650 nm for a period of 1 minute and the fluorescence is meaεured as in the preceding examples. The value obtained is compared with valueε obtained by conducting a εimilar assay with known amounts of thyroxine. In this way the amount of thyroxine in the serum εample iε quantitated. In an alternative approach baεed on the above, Reagent 6 has avidin in place of antibody for thyroxine. An additional reagent (Reagent 6A) haε antibody for thyroxine covalently linked to biotin. Reagent 5 has antibody for fluorescein in place of thyroxine and an additional reagent (Reagent 5A) has thyroxine linked covalently to fluorescein. In the asεay Reagents 5A and 6A are combined with sample and incubated. Then, Reagent 5 and 6 are added, the mixture is incubated, and the remainder of the asεay procedure iε followed. In another embodiment 2-hydroxyethyl-9,10-dibromo-anthracene is formed into a dye crystallite in a manner εimilar to that deεcribed by Gribnau. A 25mer oligonucleotide probe that recognizeε a εequence of hepatitiε B RNA iε covalently attached to the dye cryεtallite by meanε of a carbamate linking group. A second 25mer oligonucleotide probe for hepatitis B RNA is covalently linked to 9- (benzal-9H-xanthene) by means of an amide linking group. The dye crystallite has a particle εize 2 microns on the average. The oligonucleotideε are prepared by εtandard automated synthesiε technology. A sample (50 μL) from a patient suεpected of having hepatitiε B iε combined in an aqueouε aεεay medium (500 μL) at pH 7.0 with an excess of the dye crystallite and the εecond probe deεcribed above. The aεεay medium iε then incubated at 50°C for a period of 30 minuteε and the fluoreεcence iε then meaεured by irradiation at 330 nm and detection at 390 nm. The presence of hepatitiε B RNA in the εample cauεeε the dye cryεtallite and the 9- (benzal-9H-xanthene) to come into close proximity by virtue of the binding of the respective oligonucleotideε with the RNA. Upon irradiation of the medium the 9,10-dibromoanthracene is excited and converts ground εtate oxygen to εinglet oxygen. The εinglet oxygen reactε with the xanthene to give a xanthone, which is fluorescent. The fluorescence iε meaεured photometrically and the amount of light over a certain threεhold level indicateε the preεence of hepatitiε B RNA in the sample. Irradiation of the medium is conducted at room temperature and the asεay iε conducted in a homogeneous manner to yield an asεay for hepatitiε B RNA. In another embodiment the aεεay is for the determination of a particular blood group antigen on the surface of a red blood cell, namely, an A group antigen. Latex particles prepared as described above having a particle size of 150 to 500 nm are utilized. The latex particleε have an antibody for the A group antigen covalently linked to the latex particle. The particles also have the photoactive indicator precursor of formula (If) : which is dissolved in the latex. This latex particle reagent is combined in the aqueous medium (500 μl) with whole blood (100 μl) and 1X10" 4 M of a photosensitizer, which is a hydrophobic dye of the following formula: CEnCHnCHn CHOCHQCHQ The hydrophobic dye iε incorporated into the red cellε preεent in the εample. The medium is incubated at 25°C for a period of 10 minutes and then irradiated at >650 nm with a tungεten source for a period of 30 secondε. The fluorescence of the solution is then determined by irradiation at 360 nm and detection at 440 nm. The light emitted from the medium is measured and compared to the amount of light obtained in samples known to be free of A group antigen red blood cellε. Thus, the amount of light over a threshold level indicates the presence of the A blood group antigen. The present invention further encompasεes compoεitionε comprising a suspendible particle of 25 to 4000 nanometer average diameter comprising a photoactive indicator precursor. The photoactive indicator precurεor may be covalently bound to the particle matrix or may be disεolved in the matrix or diεsolved in a solvent that is disεolved in the matrix. The particleε will preferably be polymeric or be oil dropletε or veεicleε εuch aε liposomes. Where the particle is a liposome, the photoactive indicator precurεor will be aεεociated with the lipid bilayer or diεεolved in the aqueouε interior of the lipoεome. The particle will have an εbp member bound to it. Alεo encompassed are compositions comprised of two complementary sbp memberε bound to each other wherein one iε associated with a photosenεitizer and one iε associated with a photoactive indicator precursor. Another aspect of the present invention relates to kits uεeful for conveniently performing an aεεay method of the invention for determining the preεence or amount of an analyte in a sample suspected of containing the analyte. To enhance the versatility of the subject invention, the reagents can be provided in packaged combination, in the same or εeparate containerε, εo that the ratio of the reagents provides for subεtantial optimization of the method and aεsay. The reagents may each be in separate containers or variouε reagentε can be combined in one or more containerε depending on the cross-reactivity and stability of the reagents. The kit compriεeε (1) a compoεition wherein the compoεition compriεeε a εuεpendible particle compriεing a photoactive indicator precurεor, the particle having an sbp member bound to it, and (2) a photosensitizer. The photosenεitizer can be attached to an sbp member or it can be asεociated with a particle, to which an εbp member is bound. The kit can further include other separately packaged reagents for conducting an asεay including ancillary reagents, and so forth. Another embodiment of a kit in accordance with the present invention comprises in packaged combination a photoactive indicator precursor asεociated with a firεt sbp member and a photoεenεitizer capable in itε excited εtate of activating oxygen to itε singlet state associated with a second sbp member. EXAMPLES The invention is demonstrated further by the following illustrative examples. Parts and percentages used herein are by weight unless otherwise specified. Temperatures are in degrees centigrade (°C) . The following abbreviations are used in the Examples: "Amino-GATTAG" - a modified 42mer oligonucleotide having the sequence shown below: 5' -GATTAG-GATTAG-GATTAG-GATTAG-GATTAG-GATTAG- GATTAG-3' (SEQ ID NO:l) with the nucleotide (Clontech Laboratorieε, #5202-1) at the 5'-end εubεtituted aε illuεtrated below: "Biotin-30mer" - a modified 30mer oligonucleotide having the εequence εhown below: 5' -CAA-TAC-AGG-TTG-TTG-CCT-TCA-CGC- TCG-AAA-3' (SEQ ID NO:2) ; with biotin attached to a modified cytosine (5-methylcytosine) at the 5'-end through a linking group aε shown below: "CTAATC-30mer" - a modified tailed 30mer oligonucleotide having the sequence shown below: 5' -CTG-CCG-GTG-CGC-CAT-GCT-CGC-CCG-CTT- CAC-CTA-ATC-CTA-ATC-CTA-ATC-CTA-ATC-CTA- ATC-CTA-ATC-3' (SEQ ID NO:3) . "DMF" dimethyl formamide. "EDAC" l-ethyl-3- (3-dimethylaminopropyl) -carbodiimide hydrochloride. "EDTA" - ethylenediaminetetraacetic acid. "GATTAG-SH" - a modified 42mer oligonucleotide having the sequence shown below: 5' -GATTAG-GATTAG-GATTAG-GATTAG-GATTAG- GATTAG-GATTAG-3' (SEQ ID NO:4) with the 5'-end nucleotide substituted as illustrated below: "MES" - 2 - (W-morpholino) ethane sulfonic acid. "SPDP" - lΫ-εuccinimidyl 3- (2-pyridylthio) -propionate . "Sulfo-SMCC" - 4 - (lV-maleimidomethyl) cyclohexane-l - carboxylate . "TCEP" - triε-carboxyethyl phoεphine . "THF" - tetrahydrof uran . Example 1 Preparation of a Photoactive Indicator Precurεor cou ar in-1 Z_ A εolution of coumarin-1 (11.0 g, 47.5 mmol) in ethyl acetate (150 mL) waε treated with 10% Pd/C (100 mg) in a parr bottle. The εuspension waε then hydrogenated at 80 pεi and 80°C for 6 hourε. The εuεpenεion waε filtered through a bed of celite to remove the Pd/C, and the celite bed waεhed with warm ethyl acetate (100 mL) . The filtrate waε concentrated and dried under vacuo to yield 11.0 g (100%) of the 3,4-dihydrocoumarin (2.) aε an oil; •H-NMR (CDC1 3 ,250 MHz): δ 7.02 (d,J=8.5Hz,1H) ; 6.42 (dd,J=8.5Hz,1.7Hz,lH) ; 6.35 (d,J=l.7Hz,1H) ; 4.07 (q, =7.0Hz,4H) ; 3.06 (m,lH); 2.80 (dd,^=15.6Hz, J.* c =5.4Hz f lH) ; 2.51 (dd,J^ 15.6Hz, 3^=7.7Hz, 1H) ; 1.28 (d,J=7.0Hz,3H) ; 1.15 (t,J=7.0Hz,6H) ; MS(EI) calculated for C 14 H 1!1 N0 2 , 233: found 233 (M + ,40%) ; 218 (M + -CH-., 100%). A εolution of 3,4-dihydrocoumarin 2 (1.68 g, 7.20 mmol) in anhydrouε THF (20 mL) waε cooled to -78°C under argon. Lithium diiεopropylamide in THF (8.0 mL of 1.0 M, 8.0 mmol) waε added to the εtirred solution and the resultant yellow colored solution was further stirred for 1 hour. Phenyl selenyl chloride (1.50 g, 7.8 mmol) dissolved in THF (10 mL) was subεequently added into the enolate εolution. The orange color of the mixture quickly faded to yield a yellow εolution. The solution was εtirred for 3 hourε and quenched with aqueouε NH 4 C1 (10 mL of 1%) . After about 10 minuteε, dichloromethane (100 mL) waε added and the organic phaεe εeparated. The aqueouε portion waε further extracted with CH 2 C1 2 (2x20 mL) and the organic portionε combined. The combined organic portionε were waεhed with brine (20 mL) , dried over anhydrouε Na 2 S0 4 (25 g) and concentrated to yield 2.10 g of an yellow oil. The oil waε purified by chromatography on εilica gel with hexane in dichloromethane gradient to yield 1.80 g (67%) of the coumarin-3-phenyl selenide 3., aε a white powder. Crystallization from hot hexane afforded 1.30 g of 3. aε white needles, m.p. 99-101°C; -H-NMR (C β Dg,250MHz) δ 7.65 (m,2H); 6.92 (m,3H) ; 6.74 (d,J=8.0Hz,lH) ; 6.38 (d,J=l.5Hz,1H) ; 6.25 (dd,J=8.0Hz, 1.5Hz,1H) ; 3.88 (d,J=2Hz,lH) ; 3.02 (m,1H) ; 2.84 (q,J=7.0Hz,4H) ; 0.96 (d,J=7.0Hz, 3H) ; 0.80 (t,J=7.0Hz,6H) ; MS (El) calcd. for CjoHz-NOjSe 389 ; found 389 (M + , 100%) ; 232 ( ^-C^Se 70%) ; 218 (60%) ; 202 (45%) ; UV-Viε (toluene) 300 nm (4600) ; 310 nm (4600) ; 330 nm (2100) . Example 2 Preparation of a Photoactive Indicator Precurεor To a εtirred εuspension of tellurium powder (100 meεh, 13.0 g, 0.10 mol) in dry THF (150 mL) waε added a εolution of phenyl lithium (60 mL of 1.8M, 0.10 mol) in ether-hexanes. The suεpension was stirred at room temperature for 2 hours and then refluxed for 1 hour. The εuεpension was allowed to cool and water (100 mL) waε added followed by overnight stirring. Oxygen gas waε bubbled through the εuεpension for 3 hours. Methylene chloride (200 mL) was added and the organic phase separated. The aqueous phaεe waε further extracted with CH-.C1 2 (2x100 mL) and the combined portionε waεhed with brine (100 mL) and dried over anhydrouε Na^SO^ The dried εolution waε pasεed through a plug of εilica (300 g) ; the filtrate thuε obtained waε concentrated and cryεtallized from hot ethanol to yield 13.2 g of the diphenyl ditelluride 4., aε orange red needleε, m.p. 63-65%C (lit 63.5-65°C) ; MS (El) calcd for C 12 H 10 Te 2 414; found 414 (25%); 412 (45%); 410 (50%) ; 408 (40%) ; 207 (40%) . The diphenyl ditelluride 4. (1.0 g, 2.5 mmol) waε diεεolved in THF (10.0 mL) and cooled to 0°C. Bromine (125 μL, 2.5 mmol) in THF (5.0 mL) waε added and the εolution stirred at 0°C for l hour and allowed to attain room temperature. The reaction mixture waε εtirred at room temperature until no more starting material was detectable by analytical thin layer chromatography to yield compound 5.. A εolution of the 3,4-dihydrocoumarin (240 mg, 1.0 mmol) in anhydrous THF (10 mL) was cooled to -78°C under argon. Lithium diisopropyl amide (1.1 mL of 1.0 M, 1.1 mmol) in THF was added and the solution stirred at -78°C for 1 hour. A solution of 5. (3 mmol, prepared as deεcribed above) in THF waε cannulated into the eεter enolate and the mixture εtirred for 2 hourε at -78°C and then allowed to attain room temperature. The reaction mixture was quenched with aqueous NH 4 C1 (1%, 5 mL) and stirred for another 5 minutes. The reaction mixture waε then extracted with CH 2 C1 2 (3.25 mL) r and the combined organic portions washed with brine (20 mL) and dried over anhydrous Na^O, (20 g) . Concentration followed by flash chromatography (under subdued lighting) on εilica with CB-T^ gave 190 mg (43%) of an yellow oil. Cryεtallization from cyclohexane afforded 165 mg of the coumarin telluride 6. aε a light yellow colored εolid; ■ H-NMR (CDC1 3 ,250MHZ) δ 7.82 (dd,J=7.0Hz,1.2 Hz,2H); 7.31 (m,lH); 7.26 (m,2H); 6.91 (d,J=8.5Hz,1H) ; 6.38 (dd,J=8.5Hz,2.5Hz,1H) ; 6.25 (d,J=2.5Hz,lH) ; 4.05 (d,2.0Hz,1H) ; 3.33 (q,J=7.0Hz,4H) ; 3.25 (m,lH); 1.23 (d,J=7.0Hz,3H) ; 1.16 (t,J=7.0Hz,6H) ; MS (El) calcd. for C 20 H 23 NO 2 Te 439 (uεing 130 Te) ; found 439 (M + ,20%); 232 (M^-C^ e,100%) ; 217 (25%); 202 (35%); UV-Viε (toluene) 310 nm (3860) ; 330 nm (2400) ; 370 nm (510) . Example 3 Preparation of a Photoactive Indicator Precurεor A εolution of p-bromo-_V,W-dimethyl aniline (10.0 g, 50.0 mmol) in anhydrous THF (200 mL) was cooled to -78°C under argon. Into this cooled solution was carefully added t-butyl lithium (56 mL of 1.8 M, 100 mmol) in pentane, and the resulting yellow suεpenεion stirred for 1 hour at -78°C. Finely ground tellurium powder (6.50 g, 50 mmol) waε added under a stream of argon. The reaction mixture was then allowed to attain room temperature, by that time (-2 hours) most of the tellurium had diεsolved. The reaction mixture was quenched with water (20 mL) and poured into aqueouε K 3 _Fe(CN) 6 ] εolution (17 g in 200 mL, 0.052 mol) . The mixture was stirred for 1 hour and then extracted with CHjCl 2 (3x200 mL) . The combined organic portions were washed with brine (100 mL) and dried over anhydrous Na 2 S0 4 (100 g) . The dried material waε paεεed through a plug of εilica (300 g) and the filtrate concentrated to yield 12.2 g of an orange-red paεte. Cryεtallization from ethanol gave 8.6 g of the ditelluride 7_, aε an orange red powder. Another batch (2.2 g) was recovered from the mother liquor; MS (El) calculated for C-e-Hjo -jTez, 500; found 500 (20%); 498 (40%) ; 496 (45%) ; 250 (100%) ; 240 (98%) . The ditelluride 7, (1.70 g, 3.4 mmol) was disεolved in a minimum amount of anhydrouε THF and cooled to 0°C. The εolution waε treated with bromine (175 μL, 3.4 mmol) and the mixture stirred at 0°C for 3 hours to yield a solution containing the desired product 8.. The product 8. waε then cannulated under argon into a solution of the dihydro coumarin 2. (800 mg, 3.4 mmol) and lithium diisopropyl amide (3.5 mL of 1.0 M, 3.5 mmol) in THF. The resulting orange red mixture was allowed to attain room temperature and quenched with aqueous NH 4 C1 (10 mL of 1.0%) . The mixture waε εubεequently extracted with C^Cl-- (3x50 mL) and the pooled organic portion dried with brine (50 mL) and anhydrous Na 2 S0 4 . Concentration followed by flash chromatography (under subdued light) on silica with gave 510 mg of the coumarin 3- (4-dimethylamino)phenyl telluride 9., together with 110 mg of the starting dihydro coumarin 2 . The yield of 9, was 37% based upon recovered starting material; 'H-NMR (CDC1 3 ,250MHz) δ 7.65 (d,J=8.0Hz,2H) ; 6.92 (d,J=8.5Hz,lH) ; 6.52 (d,J=8.0Hz,2H) ; 6.41 (dd,J=8.5Hz,1.5Hz,1H) ; 6.24 (d,J=1.5Hz,lH) ; 4.03 (d,2Hz,lH); 3.38 (q,J=7.0Hz,4H) ; 3.25 (m,H) ; 2.95 (S,6H); 1.19 (d, =7.0Hz,3H) ; 1.14 (t,J=7.0Hz,6H) . ; MS (El) calcd. for C 22 H 28 N 2 0 2 Te, 482 (using 130 Te) ; found 482 (M + -, 20%) ; 252 (20%) ; 232 100%) ; UV-Viε (toluene) 300 nm (18000) ; 320 nm (13600) ; 330 nm (8400) . Example 4 Preparation of Photoactive Indicator Precurεor Particleε (Acceptor Beadε) A 0.3 M εolution of coumarin-3- (4-dimethylamino)phenyl telluride 9, waε prepared in degassed ethoxy ethanol by gentle warming. Ethylene glycol (1 mL) was heated to 105-110°C in a 4 mL vial. A stock latex suεpension (200 μL of 10% solids in H 2 0) was added to the vial and the mixture stirred magnetically under argon. Coumarin-3- ( -dimethylamino)phenyl telluride 9. (200 μL, 0.3 M in ethoxyethanol) was added slowly to the mixture and the resulting mixture stirred for 5 minutes, then allowed to attain room temperature under argon. After cooling, the suspension was treated with ethanol (3 mL) and transferred to a centrifuge tube. The mixture waε then centrifuged at 15,000 rpm (Sorval, SA 600 rotor) for 1 hour. The εupernatant waε carefully decanted and the pellet reεuspended in aqueous ethanol (4.0 mL) by sonication. The εuspension was centrifuged at 15,000 rpm for 1 hour. The supernatant was once again removed and the pellet was resuspended in water (4 mL) . Following a final centrifugation and removal of supernatant, the pellet was resuspended in water to a final volume of 2 mL to a yield of 10 mg/mL photoactive indicator precurεor particles suspension. Example 5 Preparation of Streptavidin-Photoactive Indicator Precursor Dyed Particles The photoactive indicator precursor particles (1 mL of 10 mg/mL) suεpenεion prepared in Example 4 above waε added to an EDAC εolution (0.5 mg/mL, 1 mL of 0.02 M phoεphate buffer, pH 6.0) cooled to 0°C. The suspension was stirred under argon for 30 minutes. After this time, the suεpenεion was added dropwise into a streptavidin solution (5 mg/mL, 1 mL) in borate buffer (0.2 M, pH 9.0) kept at ~0°C. The suεpension was stirred for 1 hour and allowed to warm up to room temperature. Water (1 mL) was added and the mixture centrifuged at 15,000 rpm for 1 hour. The supernatant waε diεcarded and the pellet εuεpended in water (4 mL) by εonication. The εample waε recentrifuged in water (4 mL) by εonication, and after a final centrifugation at 15,000 rpm for 30 minuteε, the reεultant pellet waε suεpended in water (5 mL) . Thiε gave a 2 mg/mL εuspension of streptavidin-photoactive indicator precursor particleε. The presence of streptavidin was confirmed by ^ biotin binding and quantitated to 2500 ± 250 streptavidin/particle. Example 6 Preparation of Maleimidated Dextran Photoεensitizer Particles A. Staining of particles. A dye mixture of chlorophyll-a (2.0 mM) and tetrabutyl squarate (4.0 mM) in benzyl alcohol waε prepared. Ethylene glycol (80 mL) waε placed in a 125 mL Erlenmeyer flaεk and warmed to 125°C on a laboratory hot plate. The dye mixture in benzyl alcohol (8 mL) waε then added followed immediately by stock latex suspension (10 mL of 10% εolidε) . Heating was discontinued and the flask and itε contentε allowed to attain room temperature. After cooling, the mixture waε diluted with an equal volume of ethanol and immediately centrifuged at 15,000 rpm for two hourε. The bluiεh-green εupernatant was discarded and the pellet suεpended in 50 mL of ethanol by εonication. The suspenεion waε centrifuged at 15,000 rpm for one hour and the faintly blue εupernatant decanted. The pellet waε resuspended in 50% aqueouε ethanol (50 mL) by εonication to disperse the particleε. Centrifugation waε repeated at 15,000 rpm for an hour. The εupernatant waε decanted and the pellet reεuεpended in water by εonication. Following a final centrifugation, the pelletε were reεuεpended in water to a final volume of 20 mL. B. Preparation of Maleimidated Dextran Photoεensitizer Particles. Aminodextran (500 mg) was partially maleimidated by reacting it with sulfo-SMCC (157 mg, 10 mL H 2 0) . The εulfo-SMCC waε added to a εolution of the aminodextran (in 40 mL, 0.05 M Na-,HP0 4 , pH 7.5) and the reεulting mixture was incubated for 1.5 hr. The reaction mixture was then dialyzed against MES/NaCl (2x2L, 10 mM MES, 10 mM NaCl, pH 6.0, 4°C) . The maleimidated dextran was centrifuged at 15,000 rpm for 15 minutes and the supernatant collected. The supernatant dextran solution (54 mL) was then treated with imidazole (7 mL of 1.0 M solution) in MES buffer (pH 6.0) and into this stirred εolution waε added the εtained photoεenεitizer particleε (10 mL of lOmg/mL) . After εtirring for 10 minutes the suεpenεion waε treated with EDAC (7 mmol in 10 mM pH 6.0 MES) and the εuεpension εtirred for 30 minuteε. After thiε time, SurfactAmps ® (Pierce) Tween-20 (10%, 0.780 mL) waε added to the reaction mixture for a final concentration of 0.1%. The particleε were then centrifuged at 15,000 rpm for 45 minuteε and the εupernatant diεcarded. The pellet was resuεpended in MES/NaCl (pH 6.0, 10 mM, 100 mL) by εonication. Centrifugation at 15,000 rpm for 45 minuteε, followed by pellet reεuεpenεion after discarding the supernatant, was performed twice. The maleimidated dextran photosenεitizer particles were stored in water as a 10 mg/mL suspension. Example 7 Preparation of GATTAG-Photosenεitizer Particleε. Amino-GATTAG (180 μL, 50 nmol) (prepared aε deεcribed below in Example 8) in water waε treated with 0.25M borax (50 μL) to give a pH of 9.2. SPDP (50 mg/mL in dry DMF) waε added in four aliquotε at 0, 10, 20 and 30 minuteε (3i.8 μmol total) . The reaction mixture waε allowed to εtand for 2 hourε. Ice cold ethanol (2.1 mL) waε added and the product left in the freezer overnight. The cloudy product mixture waε εplit into two Eppendorf tubeε and centrifuged at maximum εpeed for 10 minutes. The supernatant was carefully removed and the pellet disεolved in 400 μL Kfl . Into this solution was added 2.5 M acetate buffer (20 μL, 2.5M, pH 5.3) . TCEP in distilled water (10 μL, 20mM) waε added and the reduction allowed to proceed for 30 minuteε at room temperature. Abεolute ethanol (1.2 mL) waε added and the reaction mixture put in the freezer for 2 hourε. The reaction mixture waε centrifuged at full speed in the cold room and the precipitated GATTAG-SH oligonucleotide was removed as a pellet. The pellet was dissolved in 200 μL of 50 mM Na 2 HP0 4 buffer (pH 6.85) containing 20 mM EDTA. The solution was degasεed and kept under argon. Thiε εolution was then added to the maleimidated dextran photosenεitizer particleε (14.2 mg/1.5 mL) (prepared above in Example 6) and the reaction mixture allowed to εtand overnight. The mixture waε centrifuged at 15,000 rpm for 1 hour and the εupernatant diεcarded. The pellet waε reεuεpended in water (2 mL) and centrifuged at 15,000 rpm for 1 hour. The supernatant was discarded and the pellet reεuspended in water (2 mL) . After a final centrifugation the GATTAG-photosensitizer particles were stored in 2 mL of water solution as a suspension. Example 8 Assay for Detecting DNA A. The target 65mer oligonucleotide with the sequence shown below: 5' -GTG-AAG-CGG-GCG-AGC-ATG-GCG-CAC-CGG-CAG- AGC-ATT-TTC-GAG-CGT-GAA-GGC-AAC-AAC-CTG-TAT-TG-3' (SEQ ID NO:5) ; and CTAATC-30mer and amino-CATTAG were prepared on a Milligen Bioεearch DNA εyntheεizer (Model #8750) uεing εtandard solid phase phoεphoramidite methodology (see Oligonucleotide Syntheses - A Practical Approach (1984) , Gait M.J., Ed., IRL Presε Oxford.) The protocol briefly conεiεted of (a) removal with dichloroactic acid of the 5' -dimethoxytrityl group on the nucleoεide attached to the εolid εupport; (b) coupling of the incoming nucleoside, which contains a 5'-hydroxyl protecting group (preferably dimethoxytrityl) and a 3' -hydroxyl protecting group (preferably _V,W-diisopropylphoεphoramidite) , uεing tetrazole aε the catalyεt; (c) a capping εtep with acetic anhydride; and (d) iodine oxidation to convert the phosphite triester into a phoεphate trieεter. At the conclusion of the εyntheεiε ammonium hydroxide was used to (a) cleave the synthesized polynucleotide from the support; (b) remove the phoεphoryl protecting groups (β-cyanoethyl) ; and (c) to remove the base protecting groupε. The oligonucleotide was finally purified by HPLC. B. Biotin-30mer was prepared similarly as above except that the base of the laεt incoming nucleotide waε a 5-methyl-cytoεine with a protected amine-modifier (American Bioneticε, #ABN2599) as shown below: After deprotection, the free amine was reacted with biotin-LC-NHS (Pierce, #21335G) at a 1:60 molar ratio of the two reagentε in 0.1M NaHC0 3 , pH 9.0. Following incubation overnight at room temp, the reεulting oligonucleotide waε analyzed and purified on a 12% denaturing polyacrylamide gel. C. The asεay waε performed by mixing various volumes (0-80 μL of 21 nM) of target 65mer oligonucleotide with CTAATC-30mer (200 μL of 15 nM) and biotin-30mer (200 μL of 15 nM) in TRIS/EDTA/NaCl solution (pH 8.0, 100 mM, 0.1 mM, 0.30 M, reεpectively) contained in a 1.5 mL Eppendorf tube. The volumeε were made up to 0.5 mL and the solution annealed at 55°C for 30 minutes so that the 30mer probes could hybridize with their complements on the target 65mer oligonucleotide upon cooling. The reaction mixture was cooled to room temperature and then treated with the streptavidin- photoactive indicator precurεor particleε (100 μL of 100 μg/mL) followed by GATTAG-photosensitizer particles (400 μL of 100 μg/mL) . The mixture was gently vortexed and allowed to incubate for 2 hourε at room temperature. The εuεpenεion was then transferred to a 12x75 mm test tube and irradiated for 5 minutes with a Dolan-Jenner lamp (tungsten) equipped with a 610 nm cutoff filter. The sample was treated with an equal volume (1 mL) of buffer and tranεferred to a fluorometer. The fluoreεcence unitε corresponding to an excitation with a 360 NB filter and 420 NB filter emission were recorded. The resulting standard curves for two individual asεays are shown in Figure 1. Although the foregoing invention has been described in some detail by way of illustration and example for purposeε of clarity and underεtanding, it will be obviouε that certain changes or modifications may be practiced within the scope of the appended claims. \. SEQUENCE LISTING (1) GENERAL INFORMATION: (i) APPLICANT (A) ADDRESSEE: SYNTEX (U.S.A.) INC. (B) STREET: 3401 HILLVIEW AVENUE (C) CITY: PALO ALTO (D) STATE: CALIFORNIA (E) COUNTRY: USA (F) ZIP: 94304 (ii) TITLE OF INVENTION FLUORESCENT OXYGEN CHANNELING IMMUNOASSAYS (iii) NUMBER OF SEQUENCES: 5 (iv) COMPUTER READABLE FORM (A) MEDIUM TYPE: FLOPPY DISK (B) COMPUTER: IBM PC COMPATIBLE (C) OPERATING SYSTEM: PC-DOS/MS-DOS (D) SOFTWARE: PATENTIN RELEASE #1.0, VERSION #1.25 (vi) CURRENT APPLICATION DATA (A) APPLICATION NUMBER: PCT/US/ (2) INFORMATION FOR SEQ ID NO:l: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 42 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (vi) ORIGINAL SOURCE: (A) ORGANISM: synthetic (xi) SEQUENCE DESCRIPTION: SEQ ID NO:l: GATTAGGATT AGGATTAGGA TTAGGATTAG GATTAGGATT AG 42 (2) INFORMATION FOR SEQ ID NO:2: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (vi) ORIGINAL SOURCE: (A) ORGANISM: εynthetic (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2: CAATACAGGT TGTTGCCTTC ACGCTCGAAA 30 (2) INFORMATION FOR SEQ ID NO:3: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 66 baεe pairε (B) TYPE: nucleic acid (C) STRANDEDNESS: εingle (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (vi) ORIGINAL SOURCE: (A) ORGANISM: εynthetic (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3: CTGCCGGTGC GCCATGCTCG CCCGCTTCAC CTAATCCTAA TCCTAATCCT AATCCTAATC 60 CTAATC 66 (2) INFORMATION FOR SEQ ID N0:4: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 42 baεe pairε (B) TYPE: nucleic acid (C) STRANDEDNESS: εingle (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (vi) ORIGINAL SOURCE: (A) ORGANISM: synthetic (xi) SEQUENCE DESCRIPTION: SEQ ID N0:4: GATTAGGATT AGGATTAGGA TTAGGATTAG GATTAGGATT AG 42 (2) INFORMATION FOR SEQ ID NO:5: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 65 baεe pairε (B) TYPE: nucleic acid (C) STRANDEDNESS: εingle (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (vi) ORIGINAL SOURCE: (A) ORGANISM: εynthetic (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5: GTGAAGCGGG CGAGCATGGC GCACCGGCAG AGCATTTTCG AGCGTGAAGG CAACAACCTG 60 TATTG 65

Claims: WHAT IS CLAIMED IS: 1. A method for determining an analyte which iε a εpecific binding pair member (εbp), which method comprises: (a) providing in combination: (1) a medium suεpected of containing an analyte; (2) a photosensitizer capable in its excited state of generating singlet oxygen, wherein said photoεenεitizer is bound to an sbp member or is bound to or incorporated in a particle having εaid sbp member incorporated therein or bound thereto; and (3) a photoactive indicator precurεor capable of forming a photoactive indicator upon reaction with singlet oxygen, wherein said photoactive indicator precursor is bound to an εbp member or iε bound to or incorporated in a particle having εaid εbp member incorporated therein or bound thereto; (b) exciting εaid photoεenεitizer by irradiation with light; and (c) meaεuring the fluorescence of said photoactive indicator; wherein at least one of said sbp members is capable of binding directly or indirectly to said analyte or to an sbp member complementary to εaid analyte, and wherein εaid fluoreεcence iε related to the amount of εaid analyte in εaid medium. 2. The method of Claim 1 wherein εaid photoεenεitizer iε εelected from the group conεisting of ketones, polyaromatic compounds, cyanines, merocyanineε, phthalocyanineε, squarate dyes, porphyrinε, xantheneε, thiazineε and oxazineε. 3. The method of Claim 1 wherein εaid photoactive indicator haε an extinction coefficient of at leaεt 10,000 M "1 cm" 1 at itε abεorption maximum and a fluoreεcence emission quantum yield of at least 0.1. 4. The method of Claim 1 wherein neither the photosenεitizer nor the photoactive indicator precursor are bound to or incorporated in a particle and which further comprises prior to step (b) causing at least one of said photoεenεitizer and εaid photoactive indicator precurεor to become bound to a εurface by meanε of a εpecific binding pair binding. 5. The method of Claim 4 wherein a suεpendible particle compriεeε said surface, said particle being selected from the group consisting of latex particles, lipid veεicleε, oil dropletε, εilica particleε, metal solε, and dye crystallites. 6. The method of Claim 1 wherein said analyte is selected from the group consiεting of a drug, a protein, a polynucleotide, a receptor and a microorganiεm. 7. A method for determining an analyte, which method compriεeε: (A) if the analyte is a polynucleotide (a) combining in an aqueous medium; (1) εaid analyte; (2) one or more polynucleotide probeε, wherein each probe containε a nucleotide εequence complementary to a nucleotide sequence of said analyte and wherein at least one probe iε bound to a εpecific binding pair (εbp) member, or is bound to or incorporated in a particle having said sbp member incorporated therein or bound thereto, said sbp member being different from said complementary nucleotide sequence; (3) a photosenεitizer capable in its excited state of generating εinglet oxygen, wherein said photosensitizer is bound to, or is bound to or incorporated in a particle having incorporated therein or bound thereto, a nucleotide sequence complementary to a nucleotide sequence of εaid probe; and (4) a photoactive indicator precurεor capable of forming a photoactive indicator upon reaction with εinglet oxygen, wherein εaid photoactive indicator precurεor iε bound to, or iε bound to or incorporated in a particle having incorporated therein or bound thereto, an εbp member complementary to said sbp member asεociated with εaid probe; (b) irradiating εaid medium with light to excite εaid photosensitizer to generate singlet oxygen; and (c) measuring the fluorescence of said photoactive indicator; wherein said fluorescence iε related to the amount of said analyte in said medium; or (B) if the analyte is other than a polynucleotide (a) providing in combination: (1) a medium suεpected of containing an analyte; (2) a photoεenεitizer capable in itε excited εtate of generating singlet oxygen, wherein said photoεenεitizer iε bound to, or is bound to or incorporated in a particle having incorporated therein or bound thereto, a first εpecific binding pair (εbp) member; and (3) a photoactive indicator precurεor capable of forming a photoactive indicator upon reaction with εinglet oxygen, wherein εaid photoactive indicator precursor is bound to, or iε bound to or incorporated in a particle having incorporated therein or bound thereto, a εecond εbp member (b) irradiating said combination with light to excite said photosenεitizer; and (c) meaεuring the fluoreεcence of εaid photoactive indicator; wherein each εbp member iε capable of binding directly or indirectly to εaid analyte or to an εbp member complementary to said analyte, and wherein said fluorescence is related to the amount of said analyte in said medium, and wherein said photosenεitizer iε optionally part of a suspendible particle to which said first εbp member iε bound, and wherein said photoactive indicator precursor iε optionally part of a suspendible particle to which said second sbp member iε bound. 8. A composition comprising suspendible particles of average diameter of 20 to 4000 nanometers having associated therewith a photoactive indicator precurεor which reacts with singlet oxygen to form a phototactive indicator, wherein said photoactive indicator precursor contains a selenium or tellurium atom and said phototactive indicator does not contain a εelenium or tellurium atom. 9. A kit for conducting an asεay for an analyte, which kit compriεeε, in packaged combination: (a) a photoactive indicator precurεor containing a εelenium or tellurium atom, wherein εaid photoactive indicator precurεor iε bound to, or iε bound to or incorporated in a particle having incorporated therein or bound thereto, a firεt specific binding pair (sbp) member; and (b) a photosenεitizer capable in itε excited state of activating oxygen to itε singlet state, wherein said photosensitizer is bound to, or is bound to or incorporated in a particle having incorporated therein or bound thereto, a εecond εbp member, wherein said sbp members are capable of binding to said analyte or to an εbp member capable of binding εaid analyte, and wherein εaid photoactive indicator precurεor is optionally part of a suεpendible particle to which εaid firεt εbp member iε bound, and wherein εaid photoεenεitizer iε optionally part of a suspendible particle to which said εecond εbp member iε bound. 10. A binding aεεay for an analyte that iε a specific binding pair (sbp) member, which assay comprises: (a) combining a medium suspected of containing said analyte with an sbp member capable of binding directly or indirectly to εaid analyte or to an εbp member complementary to said analyte; and (b) detecting the binding of εaid εbp member to εaid analyte or said complementary sbp member, wherein εaid detection comprises exposing a photoactive indicator precurεor in εaid medium to εinglet oxygen to produce a photoactive indicator and meaεuring the fluorescence of said photoactive indicator. 11. A compound containing the following εtructure: wherein H is cis to the XR group; X is a selenium or tellurium; R iε an organic or organometallic group bound to X through an unεaturated carbon atom, a εilicon atom, or a tin atom; and A, when taken with the carbon-carbon group, formε an alicyclic ring (optionally fuεed to one or more aromatic ringε) or a heterocyclic ring; wherein, upon reaction of the compound with εinglet oxygen, the H and the XR group are replaced by a carbon-carbon double bond to yield a fluoreεcent molecule having an extinction coefficient of at least 10,000 M "1 cm" 1 at its absorption maximum and a fluorescence emiεsion quantum yield of at least 0.1. 12. The compound of Claim 11 of the following formula: wherein R is an organic or organometallic group bound to X through an unsaturated carbon atom, a silicon atom, or a tin atom; and R 1 is hydrogen or alkyl; and wherein up to four of the remaining hydrogen atoms may be replaced by alkyl or alkylene substituents which may be taken together to form one or more alicyclic or aromatic ringε.

Inventors: DAVALIAN DARIUSH, SINGH RAJENDRA, ULLMAN EDWIN F, DAVALIAN, DARIUSH, SINGH, RAJENDRA, ULLMAN, EDWIN, F.
Applicants: SYNTEX INC, SYNTEX (U.S.A.) INC.
Application year: 1994
Main classification: G01N33
IPC codes: C07D311, C12Q1, G01N33